diff --git a/src/Umbraco.Core/Cache/FastDictionaryAppCacheBase.cs b/src/Umbraco.Core/Cache/FastDictionaryAppCacheBase.cs
index 940876dc75..e0bbd57397 100644
--- a/src/Umbraco.Core/Cache/FastDictionaryAppCacheBase.cs
+++ b/src/Umbraco.Core/Cache/FastDictionaryAppCacheBase.cs
@@ -34,7 +34,7 @@ namespace Umbraco.Cms.Core.Cache
         }
 
         /// <inheritdoc />
-        public abstract object Get(string key, Func<object?> factory);
+        public abstract object? Get(string key, Func<object?> factory);
 
         /// <inheritdoc />
         public virtual IEnumerable<object> SearchByKey(string keyStartsWith)
diff --git a/src/Umbraco.Core/Cache/SafeLazy.cs b/src/Umbraco.Core/Cache/SafeLazy.cs
index e57ac21085..387e5c0271 100644
--- a/src/Umbraco.Core/Cache/SafeLazy.cs
+++ b/src/Umbraco.Core/Cache/SafeLazy.cs
@@ -27,22 +27,22 @@ namespace Umbraco.Cms.Core.Cache
             });
         }
 
-        public static object? GetSafeLazyValue(Lazy<object?> lazy, bool onlyIfValueIsCreated = false)
+        public static object? GetSafeLazyValue(Lazy<object?>? lazy, bool onlyIfValueIsCreated = false)
         {
             // if onlyIfValueIsCreated, do not trigger value creation
             // must return something, though, to differentiate from null values
-            if (onlyIfValueIsCreated && lazy.IsValueCreated == false) return ValueNotCreated;
+            if (onlyIfValueIsCreated && lazy?.IsValueCreated == false) return ValueNotCreated;
 
             // if execution has thrown then lazy.IsValueCreated is false
             // and lazy.IsValueFaulted is true (but internal) so we use our
             // own exception holder (see Lazy<T> source code) to return null
-            if (lazy.Value is ExceptionHolder) return null;
+            if (lazy?.Value is ExceptionHolder) return null;
 
             // we have a value and execution has not thrown so returning
             // here does not throw - unless we're re-entering, take care of it
             try
             {
-                return lazy.Value;
+                return lazy?.Value;
             }
             catch (InvalidOperationException e)
             {
diff --git a/src/Umbraco.Core/Composing/ComponentComposer.cs b/src/Umbraco.Core/Composing/ComponentComposer.cs
index 00bfb0b00f..54b895ce49 100644
--- a/src/Umbraco.Core/Composing/ComponentComposer.cs
+++ b/src/Umbraco.Core/Composing/ComponentComposer.cs
@@ -12,7 +12,7 @@ namespace Umbraco.Cms.Core.Composing
         /// <inheritdoc />
         public virtual void Compose(IUmbracoBuilder builder)
         {
-            builder.Components().Append<TComponent>();
+            builder.Components()?.Append<TComponent>();
         }
 
         // note: thanks to this class, a component that does not compose anything can be
diff --git a/src/Umbraco.Core/Composing/DefaultUmbracoAssemblyProvider.cs b/src/Umbraco.Core/Composing/DefaultUmbracoAssemblyProvider.cs
index 366a9bddcb..5cc38f31a7 100644
--- a/src/Umbraco.Core/Composing/DefaultUmbracoAssemblyProvider.cs
+++ b/src/Umbraco.Core/Composing/DefaultUmbracoAssemblyProvider.cs
@@ -21,7 +21,7 @@ namespace Umbraco.Cms.Core.Composing
         private List<Assembly>? _discovered;
 
         public DefaultUmbracoAssemblyProvider(
-            Assembly entryPointAssembly,
+            Assembly? entryPointAssembly,
             ILoggerFactory loggerFactory,
             IEnumerable<string>? additionalTargetAssemblies = null)
         {
diff --git a/src/Umbraco.Core/Configuration/Models/ConnectionStrings.cs b/src/Umbraco.Core/Configuration/Models/ConnectionStrings.cs
index f99670d888..56fda7bfeb 100644
--- a/src/Umbraco.Core/Configuration/Models/ConnectionStrings.cs
+++ b/src/Umbraco.Core/Configuration/Models/ConnectionStrings.cs
@@ -5,7 +5,7 @@ namespace Umbraco.Cms.Core.Configuration.Models;
 [UmbracoOptions("ConnectionStrings")]
 public class ConnectionStrings
 {
-    private string _connectionString;
+    private string? _connectionString;
 
     /// <summary>
     /// The default provider name when not present in configuration.
@@ -22,12 +22,12 @@ public class ConnectionStrings
     /// </summary>
     public const string ProviderNamePostfix = "_ProviderName";
 
-    public string Name { get; set; }
+    public string? Name { get; set; }
 
-    public string ConnectionString
+    public string? ConnectionString
     {
         get => _connectionString;
-        set => _connectionString = value.ReplaceDataDirectoryPlaceholder();
+        set => _connectionString = value?.ReplaceDataDirectoryPlaceholder();
     }
 
     public string? ProviderName { get; set; } = DefaultProviderName;
diff --git a/src/Umbraco.Core/ContentApps/DictionaryContentAppFactory.cs b/src/Umbraco.Core/ContentApps/DictionaryContentAppFactory.cs
index b1fb31d2aa..ae8a957df7 100644
--- a/src/Umbraco.Core/ContentApps/DictionaryContentAppFactory.cs
+++ b/src/Umbraco.Core/ContentApps/DictionaryContentAppFactory.cs
@@ -9,9 +9,9 @@ namespace Umbraco.Cms.Core.ContentApps
     {
         private const int Weight = -100;
 
-        private ContentApp _dictionaryApp;
+        private ContentApp? _dictionaryApp;
 
-        public ContentApp GetContentAppFor(object source, IEnumerable<IReadOnlyUserGroup> userGroups)
+        public ContentApp? GetContentAppFor(object source, IEnumerable<IReadOnlyUserGroup> userGroups)
         {
             switch (source)
             {
diff --git a/src/Umbraco.Core/DependencyInjection/IScopedServiceProvider.cs b/src/Umbraco.Core/DependencyInjection/IScopedServiceProvider.cs
index 3b5bf7aebb..d1fabe26db 100644
--- a/src/Umbraco.Core/DependencyInjection/IScopedServiceProvider.cs
+++ b/src/Umbraco.Core/DependencyInjection/IScopedServiceProvider.cs
@@ -14,6 +14,6 @@ namespace Umbraco.Cms.Core.DependencyInjection
         /// <remarks>
         /// Can be null.
         /// </remarks>
-        IServiceProvider ServiceProvider { get; }
+        IServiceProvider? ServiceProvider { get; }
     }
 }
diff --git a/src/Umbraco.Core/DependencyInjection/IUmbracoBuilder.cs b/src/Umbraco.Core/DependencyInjection/IUmbracoBuilder.cs
index 9351bb52cf..02b356a244 100644
--- a/src/Umbraco.Core/DependencyInjection/IUmbracoBuilder.cs
+++ b/src/Umbraco.Core/DependencyInjection/IUmbracoBuilder.cs
@@ -31,7 +31,7 @@ namespace Umbraco.Cms.Core.DependencyInjection
 
         IProfiler Profiler { get; }
         AppCaches AppCaches { get; }
-        TBuilder WithCollectionBuilder<TBuilder>() where TBuilder : ICollectionBuilder;
+        TBuilder? WithCollectionBuilder<TBuilder>() where TBuilder : ICollectionBuilder;
         void Build();
     }
 }
diff --git a/src/Umbraco.Core/DependencyInjection/UmbracoBuilder.CollectionBuilders.cs b/src/Umbraco.Core/DependencyInjection/UmbracoBuilder.CollectionBuilders.cs
index 1c5dddbc20..cb40974375 100644
--- a/src/Umbraco.Core/DependencyInjection/UmbracoBuilder.CollectionBuilders.cs
+++ b/src/Umbraco.Core/DependencyInjection/UmbracoBuilder.CollectionBuilders.cs
@@ -21,7 +21,7 @@ namespace Umbraco.Cms.Core.DependencyInjection
         public static IUmbracoBuilder AddComponent<T>(this IUmbracoBuilder builder)
             where T : class, IComponent
         {
-            builder.Components().Append<T>();
+            builder.Components()?.Append<T>();
             return builder;
         }
 
@@ -33,7 +33,7 @@ namespace Umbraco.Cms.Core.DependencyInjection
         public static IUmbracoBuilder AddContentApp<T>(this IUmbracoBuilder builder)
             where T : class, IContentAppFactory
         {
-            builder.ContentApps().Append<T>();
+            builder.ContentApps()?.Append<T>();
             return builder;
         }
 
@@ -45,7 +45,7 @@ namespace Umbraco.Cms.Core.DependencyInjection
         public static IUmbracoBuilder AddContentFinder<T>(this IUmbracoBuilder builder)
             where T : class, IContentFinder
         {
-            builder.ContentFinders().Append<T>();
+            builder.ContentFinders()?.Append<T>();
             return builder;
         }
 
@@ -57,7 +57,7 @@ namespace Umbraco.Cms.Core.DependencyInjection
         public static IUmbracoBuilder AddDashboard<T>(this IUmbracoBuilder builder)
             where T : class, IDashboard
         {
-            builder.Dashboards().Add<T>();
+            builder.Dashboards()?.Add<T>();
             return builder;
         }
 
@@ -69,7 +69,7 @@ namespace Umbraco.Cms.Core.DependencyInjection
         public static IUmbracoBuilder AddMediaUrlProvider<T>(this IUmbracoBuilder builder)
             where T : class, IMediaUrlProvider
         {
-            builder.MediaUrlProviders().Append<T>();
+            builder.MediaUrlProviders()?.Append<T>();
             return builder;
         }
 
@@ -81,7 +81,7 @@ namespace Umbraco.Cms.Core.DependencyInjection
         public static IUmbracoBuilder AddEmbedProvider<T>(this IUmbracoBuilder builder)
             where T : class, IEmbedProvider
         {
-            builder.EmbedProviders().Append<T>();
+            builder.EmbedProviders()?.Append<T>();
             return builder;
         }
 
@@ -97,7 +97,7 @@ namespace Umbraco.Cms.Core.DependencyInjection
         public static IUmbracoBuilder AddSection<T>(this IUmbracoBuilder builder)
             where T : class, ISection
         {
-            builder.Sections().Append<T>();
+            builder.Sections()?.Append<T>();
             return builder;
         }
 
@@ -109,7 +109,7 @@ namespace Umbraco.Cms.Core.DependencyInjection
         public static IUmbracoBuilder AddUrlProvider<T>(this IUmbracoBuilder builder)
             where T : class, IUrlProvider
         {
-            builder.UrlProviders().Append<T>();
+            builder.UrlProviders()?.Append<T>();
             return builder;
         }
     }
diff --git a/src/Umbraco.Core/DependencyInjection/UmbracoBuilder.Collections.cs b/src/Umbraco.Core/DependencyInjection/UmbracoBuilder.Collections.cs
index a0ff6104a7..f106536169 100644
--- a/src/Umbraco.Core/DependencyInjection/UmbracoBuilder.Collections.cs
+++ b/src/Umbraco.Core/DependencyInjection/UmbracoBuilder.Collections.cs
@@ -33,12 +33,12 @@ namespace Umbraco.Cms.Core.DependencyInjection
         /// </summary>
         internal static void AddAllCoreCollectionBuilders(this IUmbracoBuilder builder)
         {
-            builder.CacheRefreshers().Add(() => builder.TypeLoader.GetCacheRefreshers());
-            builder.DataEditors().Add(() => builder.TypeLoader.GetDataEditors());
-            builder.Actions().Add(() => builder .TypeLoader.GetActions());
+            builder.CacheRefreshers()?.Add(() => builder.TypeLoader.GetCacheRefreshers());
+            builder.DataEditors()?.Add(() => builder.TypeLoader.GetDataEditors());
+            builder.Actions()?.Add(() => builder .TypeLoader.GetActions());
 
             // register known content apps
-            builder.ContentApps()
+            builder.ContentApps()?
                 .Append<ListViewContentAppFactory>()
                 .Append<ContentEditorContentAppFactory>()
                 .Append<ContentInfoContentAppFactory>()
@@ -51,24 +51,24 @@ namespace Umbraco.Cms.Core.DependencyInjection
 
             // all built-in finders in the correct order,
             // devs can then modify this list on application startup
-            builder.ContentFinders()
+            builder.ContentFinders()?
                 .Append<ContentFinderByPageIdQuery>()
                 .Append<ContentFinderByUrl>()
                 .Append<ContentFinderByIdPath>()
                 /*.Append<ContentFinderByUrlAndTemplate>() // disabled, this is an odd finder */
                 .Append<ContentFinderByUrlAlias>()
                 .Append<ContentFinderByRedirectUrl>();
-            builder.EditorValidators().Add(() => builder.TypeLoader.GetTypes<IEditorValidator>());
-            builder.HealthChecks().Add(() => builder.TypeLoader.GetTypes<HealthCheck>());
-            builder.HealthCheckNotificationMethods().Add(() => builder.TypeLoader.GetTypes<IHealthCheckNotificationMethod>());
+            builder.EditorValidators()?.Add(() => builder.TypeLoader.GetTypes<IEditorValidator>());
+            builder.HealthChecks()?.Add(() => builder.TypeLoader.GetTypes<HealthCheck>());
+            builder.HealthCheckNotificationMethods()?.Add(() => builder.TypeLoader.GetTypes<IHealthCheckNotificationMethod>());
             builder.TourFilters();
-            builder.UrlProviders()
+            builder.UrlProviders()?
                 .Append<AliasUrlProvider>()
                 .Append<DefaultUrlProvider>();
-            builder.MediaUrlProviders()
+            builder.MediaUrlProviders()?
                 .Append<DefaultMediaUrlProvider>();
             // register back office sections in the order we want them rendered
-            builder.Sections()
+            builder.Sections()?
                 .Append<ContentSection>()
                 .Append<MediaSection>()
                 .Append<SettingsSection>()
@@ -79,7 +79,7 @@ namespace Umbraco.Cms.Core.DependencyInjection
                 .Append<TranslationSection>();
             builder.Components();
             // register core CMS dashboards and 3rd party types - will be ordered by weight attribute & merged with package.manifest dashboards
-            builder.Dashboards()
+            builder.Dashboards()?
                 .Add<ContentDashboard>()
                 .Add<ExamineDashboard>()
                 .Add<FormsDashboard>()
@@ -93,9 +93,9 @@ namespace Umbraco.Cms.Core.DependencyInjection
                 .Add<SettingsDashboard>()
                 .Add(builder.TypeLoader.GetTypes<IDashboard>());
             builder.DataValueReferenceFactories();
-            builder.PropertyValueConverters().Append(builder.TypeLoader.GetTypes<IPropertyValueConverter>());
-            builder.UrlSegmentProviders().Append<DefaultUrlSegmentProvider>();
-            builder.ManifestValueValidators()
+            builder.PropertyValueConverters()?.Append(builder.TypeLoader.GetTypes<IPropertyValueConverter>());
+            builder.UrlSegmentProviders()?.Append<DefaultUrlSegmentProvider>();
+            builder.ManifestValueValidators()?
                 .Add<RequiredValidator>()
                 .Add<RegexValidator>()
                 .Add<DelimitedValueValidator>()
@@ -105,7 +105,7 @@ namespace Umbraco.Cms.Core.DependencyInjection
             builder.ManifestFilters();
             builder.MediaUrlGenerators();
             // register OEmbed providers - no type scanning - all explicit opt-in of adding types, IEmbedProvider is not IDiscoverable
-            builder.EmbedProviders()
+            builder.EmbedProviders()?
                 .Append<YouTube>()
                 .Append<Twitter>()
                 .Append<Vimeo>()
@@ -119,7 +119,7 @@ namespace Umbraco.Cms.Core.DependencyInjection
                 .Append<Issuu>()
                 .Append<Hulu>()
                 .Append<Giphy>();
-            builder.SearchableTrees().Add(() => builder.TypeLoader.GetTypes<ISearchableTree>());
+            builder.SearchableTrees()?.Add(() => builder.TypeLoader.GetTypes<ISearchableTree>());
             builder.BackOfficeAssets();
         }
 
@@ -127,141 +127,141 @@ namespace Umbraco.Cms.Core.DependencyInjection
         /// Gets the actions collection builder.
         /// </summary>
         /// <param name="builder">The builder.</param>
-        public static ActionCollectionBuilder Actions(this IUmbracoBuilder builder)
+        public static ActionCollectionBuilder? Actions(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<ActionCollectionBuilder>();
 
         /// <summary>
         /// Gets the content apps collection builder.
         /// </summary>
         /// <param name="builder">The builder.</param>
-        public static ContentAppFactoryCollectionBuilder ContentApps(this IUmbracoBuilder builder)
+        public static ContentAppFactoryCollectionBuilder? ContentApps(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<ContentAppFactoryCollectionBuilder>();
 
         /// <summary>
         /// Gets the content finders collection builder.
         /// </summary>
         /// <param name="builder">The builder.</param>
-        public static ContentFinderCollectionBuilder ContentFinders(this IUmbracoBuilder builder)
+        public static ContentFinderCollectionBuilder? ContentFinders(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<ContentFinderCollectionBuilder>();
 
         /// <summary>
         /// Gets the editor validators collection builder.
         /// </summary>
         /// <param name="builder">The builder.</param>
-        public static EditorValidatorCollectionBuilder EditorValidators(this IUmbracoBuilder builder)
+        public static EditorValidatorCollectionBuilder? EditorValidators(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<EditorValidatorCollectionBuilder>();
 
         /// <summary>
         /// Gets the health checks collection builder.
         /// </summary>
         /// <param name="builder">The builder.</param>
-        public static HealthCheckCollectionBuilder HealthChecks(this IUmbracoBuilder builder)
+        public static HealthCheckCollectionBuilder? HealthChecks(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<HealthCheckCollectionBuilder>();
 
-        public static HealthCheckNotificationMethodCollectionBuilder HealthCheckNotificationMethods(this IUmbracoBuilder builder)
+        public static HealthCheckNotificationMethodCollectionBuilder? HealthCheckNotificationMethods(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<HealthCheckNotificationMethodCollectionBuilder>();
 
         /// <summary>
         /// Gets the TourFilters collection builder.
         /// </summary>
-        public static TourFilterCollectionBuilder TourFilters(this IUmbracoBuilder builder)
+        public static TourFilterCollectionBuilder? TourFilters(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<TourFilterCollectionBuilder>();
 
         /// <summary>
         /// Gets the URL providers collection builder.
         /// </summary>
         /// <param name="builder">The builder.</param>
-        public static UrlProviderCollectionBuilder UrlProviders(this IUmbracoBuilder builder)
+        public static UrlProviderCollectionBuilder? UrlProviders(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<UrlProviderCollectionBuilder>();
 
         /// <summary>
         /// Gets the media url providers collection builder.
         /// </summary>
         /// <param name="builder">The builder.</param>
-        public static MediaUrlProviderCollectionBuilder MediaUrlProviders(this IUmbracoBuilder builder)
+        public static MediaUrlProviderCollectionBuilder? MediaUrlProviders(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<MediaUrlProviderCollectionBuilder>();
 
         /// <summary>
         /// Gets the backoffice sections/applications collection builder.
         /// </summary>
         /// <param name="builder">The builder.</param>
-        public static SectionCollectionBuilder Sections(this IUmbracoBuilder builder)
+        public static SectionCollectionBuilder? Sections(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<SectionCollectionBuilder>();
 
         /// <summary>
         /// Gets the components collection builder.
         /// </summary>
-        public static ComponentCollectionBuilder Components(this IUmbracoBuilder builder)
+        public static ComponentCollectionBuilder? Components(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<ComponentCollectionBuilder>();
 
         /// <summary>
         /// Gets the backoffice dashboards collection builder.
         /// </summary>
         /// <param name="builder">The builder.</param>
-        public static DashboardCollectionBuilder Dashboards(this IUmbracoBuilder builder)
+        public static DashboardCollectionBuilder? Dashboards(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<DashboardCollectionBuilder>();
 
         /// <summary>
         /// Gets the cache refreshers collection builder.
         /// </summary>
         /// <param name="builder">The builder.</param>
-        public static CacheRefresherCollectionBuilder CacheRefreshers(this IUmbracoBuilder builder)
+        public static CacheRefresherCollectionBuilder? CacheRefreshers(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<CacheRefresherCollectionBuilder>();
 
         /// <summary>
         /// Gets the map definitions collection builder.
         /// </summary>
         /// <param name="builder">The builder.</param>
-        public static MapDefinitionCollectionBuilder MapDefinitions(this IUmbracoBuilder builder)
+        public static MapDefinitionCollectionBuilder? MapDefinitions(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<MapDefinitionCollectionBuilder>();
 
         /// <summary>
         /// Gets the data editor collection builder.
         /// </summary>
         /// <param name="builder">The builder.</param>
-        public static DataEditorCollectionBuilder DataEditors(this IUmbracoBuilder builder)
+        public static DataEditorCollectionBuilder? DataEditors(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<DataEditorCollectionBuilder>();
 
         /// <summary>
         /// Gets the data value reference factory collection builder.
         /// </summary>
         /// <param name="builder">The builder.</param>
-        public static DataValueReferenceFactoryCollectionBuilder DataValueReferenceFactories(this IUmbracoBuilder builder)
+        public static DataValueReferenceFactoryCollectionBuilder? DataValueReferenceFactories(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<DataValueReferenceFactoryCollectionBuilder>();
 
         /// <summary>
         /// Gets the property value converters collection builder.
         /// </summary>
         /// <param name="builder">The builder.</param>
-        public static PropertyValueConverterCollectionBuilder PropertyValueConverters(this IUmbracoBuilder builder)
+        public static PropertyValueConverterCollectionBuilder? PropertyValueConverters(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<PropertyValueConverterCollectionBuilder>();
 
         /// <summary>
         /// Gets the url segment providers collection builder.
         /// </summary>
         /// <param name="builder">The builder.</param>
-        public static UrlSegmentProviderCollectionBuilder UrlSegmentProviders(this IUmbracoBuilder builder)
+        public static UrlSegmentProviderCollectionBuilder? UrlSegmentProviders(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<UrlSegmentProviderCollectionBuilder>();
 
         /// <summary>
         /// Gets the validators collection builder.
         /// </summary>
         /// <param name="builder">The builder.</param>
-        internal static ManifestValueValidatorCollectionBuilder ManifestValueValidators(this IUmbracoBuilder builder)
+        internal static ManifestValueValidatorCollectionBuilder? ManifestValueValidators(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<ManifestValueValidatorCollectionBuilder>();
 
         /// <summary>
         /// Gets the manifest filter collection builder.
         /// </summary>
         /// <param name="builder">The builder.</param>
-        public static ManifestFilterCollectionBuilder ManifestFilters(this IUmbracoBuilder builder)
+        public static ManifestFilterCollectionBuilder? ManifestFilters(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<ManifestFilterCollectionBuilder>();
 
         /// <summary>
         /// Gets the content finders collection builder.
         /// </summary>
         /// <param name="builder">The builder.</param>
-        public static MediaUrlGeneratorCollectionBuilder MediaUrlGenerators(this IUmbracoBuilder builder)
+        public static MediaUrlGeneratorCollectionBuilder? MediaUrlGenerators(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<MediaUrlGeneratorCollectionBuilder>();
 
         /// <summary>
@@ -269,26 +269,26 @@ namespace Umbraco.Cms.Core.DependencyInjection
         /// </summary>
         /// <param name="builder">The builder.</param>
         [Obsolete("Use EmbedProviders() instead")]
-        public static EmbedProvidersCollectionBuilder OEmbedProviders(this IUmbracoBuilder builder)
+        public static EmbedProvidersCollectionBuilder? OEmbedProviders(this IUmbracoBuilder builder)
             => EmbedProviders(builder);
 
         /// <summary>
         /// Gets the backoffice Embed Providers collection builder.
         /// </summary>
         /// <param name="builder">The builder.</param>
-        public static EmbedProvidersCollectionBuilder EmbedProviders(this IUmbracoBuilder builder)
+        public static EmbedProvidersCollectionBuilder? EmbedProviders(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<EmbedProvidersCollectionBuilder>();
 
         /// <summary>
         /// Gets the back office searchable tree collection builder
         /// </summary>
-        public static SearchableTreeCollectionBuilder SearchableTrees(this IUmbracoBuilder builder)
+        public static SearchableTreeCollectionBuilder? SearchableTrees(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<SearchableTreeCollectionBuilder>();
 
         /// <summary>
         /// Gets the back office custom assets collection builder
         /// </summary>
-        public static CustomBackOfficeAssetsCollectionBuilder BackOfficeAssets(this IUmbracoBuilder builder)
+        public static CustomBackOfficeAssetsCollectionBuilder? BackOfficeAssets(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<CustomBackOfficeAssetsCollectionBuilder>();
     }
 }
diff --git a/src/Umbraco.Core/DependencyInjection/UmbracoBuilder.cs b/src/Umbraco.Core/DependencyInjection/UmbracoBuilder.cs
index 94b8b70c1b..3fefcbef97 100644
--- a/src/Umbraco.Core/DependencyInjection/UmbracoBuilder.cs
+++ b/src/Umbraco.Core/DependencyInjection/UmbracoBuilder.cs
@@ -49,7 +49,7 @@ namespace Umbraco.Cms.Core.DependencyInjection
 {
     public class UmbracoBuilder : IUmbracoBuilder
     {
-        private readonly Dictionary<Type, ICollectionBuilder> _builders = new Dictionary<Type, ICollectionBuilder>();
+        private readonly Dictionary<Type, ICollectionBuilder?> _builders = new Dictionary<Type, ICollectionBuilder?>();
 
         public IServiceCollection Services { get; }
 
@@ -102,17 +102,17 @@ namespace Umbraco.Cms.Core.DependencyInjection
         /// </summary>
         /// <typeparam name="TBuilder">The type of the collection builder.</typeparam>
         /// <returns>The collection builder.</returns>
-        public TBuilder WithCollectionBuilder<TBuilder>()
+        public TBuilder? WithCollectionBuilder<TBuilder>()
             where TBuilder : ICollectionBuilder
         {
             Type typeOfBuilder = typeof(TBuilder);
 
             if (_builders.TryGetValue(typeOfBuilder, out ICollectionBuilder? o))
             {
-                return (TBuilder)o;
+                return (TBuilder?)o;
             }
 
-            TBuilder builder;
+            TBuilder? builder;
 
             if (typeof(TBuilder).GetConstructor(Type.EmptyTypes) != null)
             {
@@ -121,7 +121,7 @@ namespace Umbraco.Cms.Core.DependencyInjection
             else if (typeof(TBuilder).GetConstructor(new[] { typeof(IUmbracoBuilder) }) != null)
             {
                 // Handle those collection builders which need a reference to umbraco builder i.e. DistributedLockingCollectionBuilder.
-                builder = (TBuilder)Activator.CreateInstance(typeof(TBuilder), this);
+                builder = (TBuilder?)Activator.CreateInstance(typeof(TBuilder), this);
             }
             else
             {
@@ -134,9 +134,9 @@ namespace Umbraco.Cms.Core.DependencyInjection
 
         public void Build()
         {
-            foreach (ICollectionBuilder builder in _builders.Values)
+            foreach (ICollectionBuilder? builder in _builders.Values)
             {
-                builder.RegisterWith(Services);
+                builder?.RegisterWith(Services);
             }
 
             _builders.Clear();
diff --git a/src/Umbraco.Core/Events/UserNotificationsHandler.cs b/src/Umbraco.Core/Events/UserNotificationsHandler.cs
index 61bcde6a1b..96425e644f 100644
--- a/src/Umbraco.Core/Events/UserNotificationsHandler.cs
+++ b/src/Umbraco.Core/Events/UserNotificationsHandler.cs
@@ -169,7 +169,7 @@ namespace Umbraco.Cms.Core.Events
                 SendNotification(user, entities, action, _hostingEnvironment.ApplicationMainUrl);
             }
 
-            private void SendNotification(IUser sender, IEnumerable<IContent> entities, IAction? action, Uri siteUri)
+            private void SendNotification(IUser sender, IEnumerable<IContent> entities, IAction? action, Uri? siteUri)
             {
                 if (sender == null)
                     throw new ArgumentNullException(nameof(sender));
diff --git a/src/Umbraco.Core/Exceptions/BootFailedException.cs b/src/Umbraco.Core/Exceptions/BootFailedException.cs
index 9c4e484741..eeac07869d 100644
--- a/src/Umbraco.Core/Exceptions/BootFailedException.cs
+++ b/src/Umbraco.Core/Exceptions/BootFailedException.cs
@@ -58,7 +58,7 @@ namespace Umbraco.Cms.Core.Exceptions
         /// <remarks>
         /// The exception can be null, in which case a default message is used.
         /// </remarks>
-        public static void Rethrow(BootFailedException bootFailedException)
+        public static void Rethrow(BootFailedException? bootFailedException)
         {
             if (bootFailedException == null)
                 throw new BootFailedException(DefaultMessage);
diff --git a/src/Umbraco.Core/Extensions/ConnectionStringExtensions.cs b/src/Umbraco.Core/Extensions/ConnectionStringExtensions.cs
index 6aa17055f9..6af569e514 100644
--- a/src/Umbraco.Core/Extensions/ConnectionStringExtensions.cs
+++ b/src/Umbraco.Core/Extensions/ConnectionStringExtensions.cs
@@ -18,7 +18,7 @@ namespace Umbraco.Extensions
         /// <summary>
         /// Gets a connection string from configuration with placeholders replaced.
         /// </summary>
-        public static string GetUmbracoConnectionString(
+        public static string? GetUmbracoConnectionString(
             this IConfiguration configuration,
             string connectionStringName = Constants.System.UmbracoConnectionName) =>
             configuration.GetConnectionString(connectionStringName).ReplaceDataDirectoryPlaceholder();
@@ -26,7 +26,7 @@ namespace Umbraco.Extensions
         /// <summary>
         /// Replaces instances of the |DataDirectory| placeholder in a string with the value of AppDomain DataDirectory.
         /// </summary>
-        public static string ReplaceDataDirectoryPlaceholder(this string input)
+        public static string? ReplaceDataDirectoryPlaceholder(this string input)
         {
             var dataDirectory = AppDomain.CurrentDomain.GetData("DataDirectory")?.ToString();
             return input?.Replace(ConnectionStrings.DataDirectoryPlaceholder, dataDirectory);
diff --git a/src/Umbraco.Core/Extensions/PublishedContentExtensions.cs b/src/Umbraco.Core/Extensions/PublishedContentExtensions.cs
index 64ec9f174b..63dfd5b884 100644
--- a/src/Umbraco.Core/Extensions/PublishedContentExtensions.cs
+++ b/src/Umbraco.Core/Extensions/PublishedContentExtensions.cs
@@ -1054,7 +1054,7 @@ namespace Umbraco.Extensions
         /// <remarks>
         ///   <para>Note that in V7 this method also return the content node self.</para>
         /// </remarks>
-        public static IEnumerable<IPublishedContent>? Siblings(this IPublishedContent content, IPublishedSnapshot publishedSnapshot, IVariationContextAccessor variationContextAccessor, string? culture = null)
+        public static IEnumerable<IPublishedContent>? Siblings(this IPublishedContent content, IPublishedSnapshot? publishedSnapshot, IVariationContextAccessor variationContextAccessor, string? culture = null)
         {
             return SiblingsAndSelf(content, publishedSnapshot, variationContextAccessor, culture)?.Where(x => x.Id != content.Id);
         }
@@ -1071,7 +1071,7 @@ namespace Umbraco.Extensions
         /// <remarks>
         ///   <para>Note that in V7 this method also return the content node self.</para>
         /// </remarks>
-        public static IEnumerable<IPublishedContent>? SiblingsOfType(this IPublishedContent content, IPublishedSnapshot publishedSnapshot, IVariationContextAccessor variationContextAccessor, string contentTypeAlias, string? culture = null)
+        public static IEnumerable<IPublishedContent>? SiblingsOfType(this IPublishedContent content, IPublishedSnapshot? publishedSnapshot, IVariationContextAccessor variationContextAccessor, string contentTypeAlias, string? culture = null)
         {
             return SiblingsAndSelfOfType(content, publishedSnapshot, variationContextAccessor, contentTypeAlias, culture)?.Where(x => x.Id != content.Id);
         }
@@ -1088,7 +1088,7 @@ namespace Umbraco.Extensions
         /// <remarks>
         ///   <para>Note that in V7 this method also return the content node self.</para>
         /// </remarks>
-        public static IEnumerable<T>? Siblings<T>(this IPublishedContent content, IPublishedSnapshot publishedSnapshot, IVariationContextAccessor variationContextAccessor, string? culture = null)
+        public static IEnumerable<T>? Siblings<T>(this IPublishedContent content, IPublishedSnapshot? publishedSnapshot, IVariationContextAccessor variationContextAccessor, string? culture = null)
             where T : class, IPublishedContent
         {
             return SiblingsAndSelf<T>(content, publishedSnapshot, variationContextAccessor, culture)?.Where(x => x.Id != content.Id);
@@ -1102,11 +1102,11 @@ namespace Umbraco.Extensions
         /// <param name="variationContextAccessor">Variation context accessor.</param>
         /// <param name="culture">The specific culture to filter for. If null is used the current culture is used. (Default is null)</param>
         /// <returns>The siblings of the content including the node itself.</returns>
-        public static IEnumerable<IPublishedContent>? SiblingsAndSelf(this IPublishedContent content, IPublishedSnapshot publishedSnapshot, IVariationContextAccessor variationContextAccessor, string? culture = null)
+        public static IEnumerable<IPublishedContent>? SiblingsAndSelf(this IPublishedContent content, IPublishedSnapshot? publishedSnapshot, IVariationContextAccessor variationContextAccessor, string? culture = null)
         {
             return content.Parent != null
                 ? content.Parent.Children(variationContextAccessor, culture)
-                : publishedSnapshot.Content.GetAtRoot().WhereIsInvariantOrHasCulture(variationContextAccessor, culture);
+                : publishedSnapshot?.Content.GetAtRoot().WhereIsInvariantOrHasCulture(variationContextAccessor, culture);
         }
 
         /// <summary>
@@ -1118,11 +1118,11 @@ namespace Umbraco.Extensions
         /// <param name="culture">The specific culture to filter for. If null is used the current culture is used. (Default is null)</param>
         /// <param name="contentTypeAlias">The content type alias.</param>
         /// <returns>The siblings of the content including the node itself, of the given content type.</returns>
-        public static IEnumerable<IPublishedContent>? SiblingsAndSelfOfType(this IPublishedContent content, IPublishedSnapshot publishedSnapshot, IVariationContextAccessor variationContextAccessor, string contentTypeAlias, string? culture = null)
+        public static IEnumerable<IPublishedContent>? SiblingsAndSelfOfType(this IPublishedContent content, IPublishedSnapshot? publishedSnapshot, IVariationContextAccessor variationContextAccessor, string contentTypeAlias, string? culture = null)
         {
             return content.Parent != null
                 ? content.Parent.ChildrenOfType(variationContextAccessor, contentTypeAlias, culture)
-                : publishedSnapshot.Content.GetAtRoot().OfTypes(contentTypeAlias).WhereIsInvariantOrHasCulture(variationContextAccessor, culture);
+                : publishedSnapshot?.Content.GetAtRoot().OfTypes(contentTypeAlias).WhereIsInvariantOrHasCulture(variationContextAccessor, culture);
         }
 
         /// <summary>
@@ -1134,12 +1134,12 @@ namespace Umbraco.Extensions
         /// <param name="variationContextAccessor">Variation context accessor.</param>
         /// <param name="culture">The specific culture to filter for. If null is used the current culture is used. (Default is null)</param>
         /// <returns>The siblings of the content including the node itself, of the given content type.</returns>
-        public static IEnumerable<T>? SiblingsAndSelf<T>(this IPublishedContent content, IPublishedSnapshot publishedSnapshot, IVariationContextAccessor variationContextAccessor, string? culture = null)
+        public static IEnumerable<T>? SiblingsAndSelf<T>(this IPublishedContent content, IPublishedSnapshot? publishedSnapshot, IVariationContextAccessor variationContextAccessor, string? culture = null)
             where T : class, IPublishedContent
         {
             return content.Parent != null
                 ? content.Parent.Children<T>(variationContextAccessor, culture)
-                : publishedSnapshot.Content.GetAtRoot().OfType<T>().WhereIsInvariantOrHasCulture(variationContextAccessor, culture);
+                : publishedSnapshot?.Content.GetAtRoot().OfType<T>().WhereIsInvariantOrHasCulture(variationContextAccessor, culture);
         }
 
         #endregion
diff --git a/src/Umbraco.Core/Features/UmbracoFeatures.cs b/src/Umbraco.Core/Features/UmbracoFeatures.cs
index 8f08d25357..5b6bfd7bfb 100644
--- a/src/Umbraco.Core/Features/UmbracoFeatures.cs
+++ b/src/Umbraco.Core/Features/UmbracoFeatures.cs
@@ -29,7 +29,7 @@ namespace Umbraco.Cms.Core.Features
         /// <summary>
         /// Determines whether a controller is enabled.
         /// </summary>
-        public bool IsControllerEnabled(Type feature)
+        public bool IsControllerEnabled(Type? feature)
         {
             if (typeof(IUmbracoFeature).IsAssignableFrom(feature))
                 return Disabled.Controllers.Contains(feature) == false;
diff --git a/src/Umbraco.Core/HealthChecks/Checks/Security/BaseHttpHeaderCheck.cs b/src/Umbraco.Core/HealthChecks/Checks/Security/BaseHttpHeaderCheck.cs
index bb60fd353c..daeea79f02 100644
--- a/src/Umbraco.Core/HealthChecks/Checks/Security/BaseHttpHeaderCheck.cs
+++ b/src/Umbraco.Core/HealthChecks/Checks/Security/BaseHttpHeaderCheck.cs
@@ -85,7 +85,7 @@ namespace Umbraco.Cms.Core.HealthChecks.Checks.Security
             var success = false;
 
             // Access the site home page and check for the click-jack protection header or meta tag
-            var url = _hostingEnvironment.ApplicationMainUrl.GetLeftPart(UriPartial.Authority);
+            var url = _hostingEnvironment.ApplicationMainUrl?.GetLeftPart(UriPartial.Authority);
 
             try
             {
@@ -106,7 +106,7 @@ namespace Umbraco.Cms.Core.HealthChecks.Checks.Security
             }
             catch (Exception ex)
             {
-                message = _textService.Localize("healthcheck","healthCheckInvalidUrl", new[] { url.ToString(), ex.Message });
+                message = _textService.Localize("healthcheck","healthCheckInvalidUrl", new[] { url?.ToString(), ex.Message });
             }
 
             return
diff --git a/src/Umbraco.Core/HealthChecks/Checks/Security/ExcessiveHeadersCheck.cs b/src/Umbraco.Core/HealthChecks/Checks/Security/ExcessiveHeadersCheck.cs
index dbbf6b701f..99729286c5 100644
--- a/src/Umbraco.Core/HealthChecks/Checks/Security/ExcessiveHeadersCheck.cs
+++ b/src/Umbraco.Core/HealthChecks/Checks/Security/ExcessiveHeadersCheck.cs
@@ -53,7 +53,7 @@ namespace Umbraco.Cms.Core.HealthChecks.Checks.Security
         {
             string message;
             var success = false;
-            var url = _hostingEnvironment.ApplicationMainUrl.GetLeftPart(UriPartial.Authority);
+            var url = _hostingEnvironment.ApplicationMainUrl?.GetLeftPart(UriPartial.Authority);
 
             // Access the site home page and check for the headers
             var request = new HttpRequestMessage(HttpMethod.Head, url);
@@ -80,7 +80,7 @@ namespace Umbraco.Cms.Core.HealthChecks.Checks.Security
             }
             catch (Exception ex)
             {
-                message = _textService.Localize("healthcheck","healthCheckInvalidUrl", new[] { url.ToString(), ex.Message });
+                message = _textService.Localize("healthcheck","healthCheckInvalidUrl", new[] { url?.ToString(), ex.Message });
             }
 
             return
diff --git a/src/Umbraco.Core/Hosting/IHostingEnvironment.cs b/src/Umbraco.Core/Hosting/IHostingEnvironment.cs
index dedf809230..5b761211ac 100644
--- a/src/Umbraco.Core/Hosting/IHostingEnvironment.cs
+++ b/src/Umbraco.Core/Hosting/IHostingEnvironment.cs
@@ -85,6 +85,6 @@ namespace Umbraco.Cms.Core.Hosting
         /// <summary>
         /// Ensures that the application know its main Url.
         /// </summary>
-        void EnsureApplicationMainUrl(Uri currentApplicationUrl);
+        void EnsureApplicationMainUrl(Uri? currentApplicationUrl);
     }
 }
diff --git a/src/Umbraco.Core/IO/FileSystemExtensions.cs b/src/Umbraco.Core/IO/FileSystemExtensions.cs
index eb5edf127d..354ab33b2f 100644
--- a/src/Umbraco.Core/IO/FileSystemExtensions.cs
+++ b/src/Umbraco.Core/IO/FileSystemExtensions.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using System.Security.Cryptography;
 using System.Text;
@@ -101,7 +102,7 @@ namespace Umbraco.Extensions
         /// <returns>
         /// <c>true</c> if the <see cref="IFileProvider" /> was successfully created; otherwise, <c>false</c>.
         /// </returns>
-        public static bool TryCreateFileProvider(this IFileSystem fileSystem, out IFileProvider? fileProvider)
+        public static bool TryCreateFileProvider(this IFileSystem fileSystem, [MaybeNullWhen(false)] out IFileProvider fileProvider)
         {
             fileProvider = fileSystem switch
             {
diff --git a/src/Umbraco.Core/Install/InstallSteps/TelemetryIdentifierStep.cs b/src/Umbraco.Core/Install/InstallSteps/TelemetryIdentifierStep.cs
index 5263ac935f..15286d249f 100644
--- a/src/Umbraco.Core/Install/InstallSteps/TelemetryIdentifierStep.cs
+++ b/src/Umbraco.Core/Install/InstallSteps/TelemetryIdentifierStep.cs
@@ -39,7 +39,7 @@ namespace Umbraco.Cms.Core.Install.InstallSteps
         public override Task<InstallSetupResult?> ExecuteAsync(object model)
         {
             _siteIdentifierService.TryCreateSiteIdentifier(out _);
-            return Task.FromResult<InstallSetupResult>(null);
+            return Task.FromResult<InstallSetupResult?>(null);
         }
 
         public override bool RequiresExecution(object model)
diff --git a/src/Umbraco.Core/InstallLog.cs b/src/Umbraco.Core/InstallLog.cs
index 245e917771..3d8ab26af9 100644
--- a/src/Umbraco.Core/InstallLog.cs
+++ b/src/Umbraco.Core/InstallLog.cs
@@ -13,10 +13,10 @@ namespace Umbraco.Cms.Core
         public int VersionPatch { get; }
         public string VersionComment { get; }
         public string Error { get; }
-        public string UserAgent { get; }
+        public string? UserAgent { get; }
         public string DbProvider { get; set; }
 
-        public InstallLog(Guid installId, bool isUpgrade, bool installCompleted, DateTime timestamp, int versionMajor, int versionMinor, int versionPatch, string versionComment, string error, string userAgent, string dbProvider)
+        public InstallLog(Guid installId, bool isUpgrade, bool installCompleted, DateTime timestamp, int versionMajor, int versionMinor, int versionPatch, string versionComment, string error, string? userAgent, string dbProvider)
         {
             InstallId = installId;
             IsUpgrade = isUpgrade;
diff --git a/src/Umbraco.Core/Logging/IProfiler.cs b/src/Umbraco.Core/Logging/IProfiler.cs
index d64cb49362..4b2bf6fc48 100644
--- a/src/Umbraco.Core/Logging/IProfiler.cs
+++ b/src/Umbraco.Core/Logging/IProfiler.cs
@@ -14,7 +14,7 @@ namespace Umbraco.Cms.Core.Logging
         /// <param name="name">The name of the step.</param>
         /// <returns>A step.</returns>
         /// <remarks>The returned <see cref="IDisposable"/> is meant to be used within a <c>using (...) {{ ... }}</c> block.</remarks>
-        IDisposable Step(string name);
+        IDisposable? Step(string name);
 
         /// <summary>
         /// Starts the profiler.
diff --git a/src/Umbraco.Core/Logging/ProfilerExtensions.cs b/src/Umbraco.Core/Logging/ProfilerExtensions.cs
index f3c18a0231..67739c2f38 100644
--- a/src/Umbraco.Core/Logging/ProfilerExtensions.cs
+++ b/src/Umbraco.Core/Logging/ProfilerExtensions.cs
@@ -13,7 +13,7 @@ namespace Umbraco.Cms.Core.Logging
         /// <param name="name">The name of the step.</param>
         /// <returns>A step.</returns>
         /// <remarks>The returned <see cref="IDisposable"/> is meant to be used within a <c>using (...) {{ ... }}</c> block.</remarks>
-        internal static IDisposable Step<T>(this IProfiler profiler, string name)
+        internal static IDisposable? Step<T>(this IProfiler profiler, string name)
         {
             if (profiler == null) throw new ArgumentNullException(nameof(profiler));
             return profiler.Step(typeof (T), name);
@@ -28,7 +28,7 @@ namespace Umbraco.Cms.Core.Logging
         /// <param name="name">The name of the step.</param>
         /// <returns>A step.</returns>
         /// <remarks>The returned <see cref="IDisposable"/> is meant to be used within a <c>using (...) {{ ... }}</c> block.</remarks>
-        internal static IDisposable Step(this IProfiler profiler, Type reporting, string name)
+        internal static IDisposable? Step(this IProfiler profiler, Type reporting, string name)
         {
             if (profiler == null) throw new ArgumentNullException(nameof(profiler));
             if (reporting == null) throw new ArgumentNullException(nameof(reporting));
diff --git a/src/Umbraco.Core/Macros/MacroPropertyModel.cs b/src/Umbraco.Core/Macros/MacroPropertyModel.cs
index 1b59992f32..643d154f21 100644
--- a/src/Umbraco.Core/Macros/MacroPropertyModel.cs
+++ b/src/Umbraco.Core/Macros/MacroPropertyModel.cs
@@ -2,14 +2,16 @@
 {
     public class MacroPropertyModel
     {
-        public string? Key { get; set; }
+        public string Key { get; set; }
 
         public string? Value { get; set; }
 
         public string? Type { get; set; }
 
         public MacroPropertyModel()
-        { }
+        {
+            Key = string.Empty;
+        }
 
         public MacroPropertyModel(string key, string value)
         {
diff --git a/src/Umbraco.Core/Models/ContentModel.cs b/src/Umbraco.Core/Models/ContentModel.cs
index e62f51fd16..cead39f019 100644
--- a/src/Umbraco.Core/Models/ContentModel.cs
+++ b/src/Umbraco.Core/Models/ContentModel.cs
@@ -11,7 +11,7 @@ namespace Umbraco.Cms.Core.Models
         /// <summary>
         /// Initializes a new instance of the <see cref="ContentModel"/> class with a content.
         /// </summary>
-        public ContentModel(IPublishedContent content) => Content = content ?? throw new ArgumentNullException(nameof(content));
+        public ContentModel(IPublishedContent? content) => Content = content ?? throw new ArgumentNullException(nameof(content));
 
         /// <summary>
         /// Gets the content.
diff --git a/src/Umbraco.Core/Models/ContentType.cs b/src/Umbraco.Core/Models/ContentType.cs
index 92c1b6cfe6..9c21cf5e80 100644
--- a/src/Umbraco.Core/Models/ContentType.cs
+++ b/src/Umbraco.Core/Models/ContentType.cs
@@ -64,8 +64,8 @@ namespace Umbraco.Cms.Core.Models
         ///     we should not store direct entity
         /// </summary>
         [IgnoreDataMember]
-        public ITemplate DefaultTemplate =>
-            AllowedTemplates.FirstOrDefault(x => x != null && x.Id == DefaultTemplateId);
+        public ITemplate? DefaultTemplate =>
+            AllowedTemplates?.FirstOrDefault(x => x != null && x.Id == DefaultTemplateId);
 
 
         [DataMember]
@@ -82,14 +82,14 @@ namespace Umbraco.Cms.Core.Models
         ///     we should not store direct entity
         /// </summary>
         [DataMember]
-        public IEnumerable<ITemplate> AllowedTemplates
+        public IEnumerable<ITemplate>? AllowedTemplates
         {
             get => _allowedTemplates;
             set
             {
                 SetPropertyValueAndDetectChanges(value, ref _allowedTemplates, nameof(AllowedTemplates), TemplateComparer);
 
-                if (_allowedTemplates.Any(x => x.Id == _defaultTemplate) == false)
+                if (_allowedTemplates?.Any(x => x.Id == _defaultTemplate) == false)
                 {
                     DefaultTemplateId = 0;
                 }
@@ -170,6 +170,6 @@ namespace Umbraco.Cms.Core.Models
             (IContentType)DeepCloneWithResetIdentities(newAlias);
 
         /// <inheritdoc/>
-        public override bool IsDirty() => base.IsDirty() || HistoryCleanup.IsDirty();
+        public override bool IsDirty() => base.IsDirty() || (HistoryCleanup?.IsDirty() ?? false);
     }
 }
diff --git a/src/Umbraco.Core/Models/Mapping/ContentTypeMapDefinition.cs b/src/Umbraco.Core/Models/Mapping/ContentTypeMapDefinition.cs
index 6a2dd0d305..2610867a79 100644
--- a/src/Umbraco.Core/Models/Mapping/ContentTypeMapDefinition.cs
+++ b/src/Umbraco.Core/Models/Mapping/ContentTypeMapDefinition.cs
@@ -157,7 +157,7 @@ namespace Umbraco.Cms.Core.Models.Mapping
             }
 
             // We need to reset the dirty properties, because it is otherwise true, just because the json serializer has set properties
-            target.HistoryCleanup.ResetDirtyProperties(false);
+            target.HistoryCleanup!.ResetDirtyProperties(false);
             if (target.HistoryCleanup.PreventCleanup != source.HistoryCleanup.PreventCleanup)
             {
                 target.HistoryCleanup.PreventCleanup = source.HistoryCleanup.PreventCleanup;
@@ -558,8 +558,8 @@ namespace Umbraco.Cms.Core.Models.Mapping
 
             target.AllowedAsRoot = source.AllowAsRoot;
 
-            bool allowedContentTypesUnchanged = target.AllowedContentTypes.Select(x => x.Id.Value)
-                .SequenceEqual(source.AllowedContentTypes);
+            bool allowedContentTypesUnchanged = target.AllowedContentTypes?.Select(x => x.Id.Value)
+                .SequenceEqual(source.AllowedContentTypes) ?? false;
 
             if (allowedContentTypesUnchanged is false)
             {
@@ -617,7 +617,7 @@ namespace Umbraco.Cms.Core.Models.Mapping
 
                 // ensure no duplicate alias, then assign the group properties collection
                 EnsureUniqueAliases(destProperties);
-                if (destGroup is not null && (destGroup.PropertyTypes.SupportsPublishing != isPublishing || destGroup.PropertyTypes.SequenceEqual(destProperties) is false))
+                if (destGroup is not null && (destGroup.PropertyTypes?.SupportsPublishing != isPublishing || destGroup.PropertyTypes.SequenceEqual(destProperties) is false))
                 {
                     destGroup.PropertyTypes = new PropertyTypeCollection(isPublishing, destProperties);
                     destGroups.Add(destGroup);
diff --git a/src/Umbraco.Core/Models/Mapping/DictionaryMapDefinition.cs b/src/Umbraco.Core/Models/Mapping/DictionaryMapDefinition.cs
index f355cba47d..6d46ffc673 100644
--- a/src/Umbraco.Core/Models/Mapping/DictionaryMapDefinition.cs
+++ b/src/Umbraco.Core/Models/Mapping/DictionaryMapDefinition.cs
@@ -15,7 +15,7 @@ namespace Umbraco.Cms.Core.Models.Mapping
     public class DictionaryMapDefinition : IMapDefinition
     {
         private readonly ILocalizationService _localizationService;
-        private readonly CommonMapper _commonMapper;
+        private readonly CommonMapper? _commonMapper;
 
         [Obsolete("Use the constructor with the CommonMapper")]
         public DictionaryMapDefinition(ILocalizationService localizationService)
diff --git a/src/Umbraco.Core/Models/Mapping/MemberTabsAndPropertiesMapper.cs b/src/Umbraco.Core/Models/Mapping/MemberTabsAndPropertiesMapper.cs
index 82631776ba..9bb53cfc9e 100644
--- a/src/Umbraco.Core/Models/Mapping/MemberTabsAndPropertiesMapper.cs
+++ b/src/Umbraco.Core/Models/Mapping/MemberTabsAndPropertiesMapper.cs
@@ -121,7 +121,7 @@ namespace Umbraco.Cms.Core.Models.Mapping
                 // check if this property is flagged as sensitive
                 var isSensitiveProperty = memberType?.IsSensitiveProperty(prop.Alias) ?? false;
                 // check permissions for viewing sensitive data
-                if (isSensitiveProperty && (_backofficeSecurityAccessor.BackOfficeSecurity.CurrentUser.HasAccessToSensitiveData() == false))
+                if (isSensitiveProperty && (_backofficeSecurityAccessor.BackOfficeSecurity?.CurrentUser?.HasAccessToSensitiveData() == false))
                 {
                     // mark this property as sensitive
                     prop.IsSensitive = true;
diff --git a/src/Umbraco.Core/Models/PartialViewMacroModel.cs b/src/Umbraco.Core/Models/PartialViewMacroModel.cs
index 1ab2078a76..662894b39f 100644
--- a/src/Umbraco.Core/Models/PartialViewMacroModel.cs
+++ b/src/Umbraco.Core/Models/PartialViewMacroModel.cs
@@ -11,9 +11,9 @@ namespace Umbraco.Cms.Core.Models
 
         public PartialViewMacroModel(IPublishedContent page,
             int macroId,
-            string macroAlias,
-            string macroName,
-            IDictionary<string, object> macroParams)
+            string? macroAlias,
+            string? macroName,
+            IDictionary<string, object?> macroParams)
         {
             Content = page;
             MacroParameters = macroParams;
@@ -23,9 +23,9 @@ namespace Umbraco.Cms.Core.Models
         }
 
         public IPublishedContent Content { get; }
-        public string MacroName { get; }
-        public string MacroAlias { get; }
+        public string? MacroName { get; }
+        public string? MacroAlias { get; }
         public int MacroId { get; }
-        public IDictionary<string, object> MacroParameters { get; }
+        public IDictionary<string, object?> MacroParameters { get; }
     }
 }
diff --git a/src/Umbraco.Core/Models/PartialViewMacroModelExtensions.cs b/src/Umbraco.Core/Models/PartialViewMacroModelExtensions.cs
index 2bc1714dbd..aea801719f 100644
--- a/src/Umbraco.Core/Models/PartialViewMacroModelExtensions.cs
+++ b/src/Umbraco.Core/Models/PartialViewMacroModelExtensions.cs
@@ -16,7 +16,7 @@ namespace Umbraco.Extensions
         /// <returns>Parameter value if available, the default value that was passed otherwise.</returns>
         public static T? GetParameterValue<T>(this PartialViewMacroModel partialViewMacroModel, string parameterAlias, T defaultValue)
         {
-            if (partialViewMacroModel.MacroParameters.ContainsKey(parameterAlias) == false || string.IsNullOrEmpty(partialViewMacroModel.MacroParameters[parameterAlias].ToString()))
+            if (partialViewMacroModel.MacroParameters.ContainsKey(parameterAlias) == false || string.IsNullOrEmpty(partialViewMacroModel.MacroParameters[parameterAlias]?.ToString()))
                 return defaultValue;
 
             var attempt = partialViewMacroModel.MacroParameters[parameterAlias].TryConvertTo(typeof(T));
diff --git a/src/Umbraco.Core/Models/PublishedContent/ModelType.cs b/src/Umbraco.Core/Models/PublishedContent/ModelType.cs
index c5f5731b0c..0de838fa0e 100644
--- a/src/Umbraco.Core/Models/PublishedContent/ModelType.cs
+++ b/src/Umbraco.Core/Models/PublishedContent/ModelType.cs
@@ -50,25 +50,25 @@ namespace Umbraco.Cms.Core.Models.PublishedContent
         /// <param name="type">The type.</param>
         /// <param name="modelTypes">The model types map.</param>
         /// <returns>The actual CLR type.</returns>
-        public static Type Map(Type type, Dictionary<string, Type> modelTypes)
+        public static Type Map(Type type, Dictionary<string, Type>? modelTypes)
             => Map(type, modelTypes, false);
 
-        public static Type Map(Type type, Dictionary<string, Type> modelTypes, bool dictionaryIsInvariant)
+        public static Type Map(Type type, Dictionary<string, Type>? modelTypes, bool dictionaryIsInvariant)
         {
             // it may be that senders forgot to send an invariant dictionary (garbage-in)
-            if (!dictionaryIsInvariant)
+            if (modelTypes is not null && !dictionaryIsInvariant)
                 modelTypes = new Dictionary<string, Type>(modelTypes, StringComparer.InvariantCultureIgnoreCase);
 
             if (type is ModelType modelType)
             {
-                if (modelTypes.TryGetValue(modelType.ContentTypeAlias, out var actualType))
+                if (modelTypes?.TryGetValue(modelType.ContentTypeAlias, out var actualType) ?? false)
                     return actualType;
                 throw new InvalidOperationException($"Don't know how to map ModelType with content type alias \"{modelType.ContentTypeAlias}\".");
             }
 
             if (type is ModelTypeArrayType arrayType)
             {
-                if (modelTypes.TryGetValue(arrayType.ContentTypeAlias, out var actualType))
+                if (modelTypes?.TryGetValue(arrayType.ContentTypeAlias, out var actualType) ?? false)
                     return actualType.MakeArrayType();
                 throw new InvalidOperationException($"Don't know how to map ModelType with content type alias \"{arrayType.ContentTypeAlias}\".");
             }
diff --git a/src/Umbraco.Core/Models/RelationItem.cs b/src/Umbraco.Core/Models/RelationItem.cs
index f4e7e30aaf..75344914f0 100644
--- a/src/Umbraco.Core/Models/RelationItem.cs
+++ b/src/Umbraco.Core/Models/RelationItem.cs
@@ -17,7 +17,7 @@ namespace Umbraco.Cms.Core.Models
         public string? NodeName { get; set; }
 
         [DataMember(Name = "type")]
-        public string NodeType { get; set; }
+        public string? NodeType { get; set; }
 
         [DataMember(Name = "udi")]
         public Udi NodeUdi => Udi.Create(NodeType, NodeKey);
diff --git a/src/Umbraco.Core/Net/IUserAgentProvider.cs b/src/Umbraco.Core/Net/IUserAgentProvider.cs
index fdca8c1dbf..ba4f61b897 100644
--- a/src/Umbraco.Core/Net/IUserAgentProvider.cs
+++ b/src/Umbraco.Core/Net/IUserAgentProvider.cs
@@ -2,6 +2,6 @@ namespace Umbraco.Cms.Core.Net
 {
     public interface IUserAgentProvider
     {
-        string GetUserAgent();
+        string? GetUserAgent();
     }
 }
diff --git a/src/Umbraco.Core/Notifications/MemberTwoFactorRequestedNotification.cs b/src/Umbraco.Core/Notifications/MemberTwoFactorRequestedNotification.cs
index 980a531ffd..e06de2624e 100644
--- a/src/Umbraco.Core/Notifications/MemberTwoFactorRequestedNotification.cs
+++ b/src/Umbraco.Core/Notifications/MemberTwoFactorRequestedNotification.cs
@@ -4,11 +4,11 @@ namespace Umbraco.Cms.Core.Notifications
 {
     public class MemberTwoFactorRequestedNotification : INotification
     {
-        public MemberTwoFactorRequestedNotification(Guid memberKey)
+        public MemberTwoFactorRequestedNotification(Guid? memberKey)
         {
             MemberKey = memberKey;
         }
 
-        public Guid MemberKey { get; }
+        public Guid? MemberKey { get; }
     }
 }
diff --git a/src/Umbraco.Core/PublishedCache/IPublishedSnapshotService.cs b/src/Umbraco.Core/PublishedCache/IPublishedSnapshotService.cs
index f4416f85ac..210739c6a2 100644
--- a/src/Umbraco.Core/PublishedCache/IPublishedSnapshotService.cs
+++ b/src/Umbraco.Core/PublishedCache/IPublishedSnapshotService.cs
@@ -31,7 +31,7 @@ namespace Umbraco.Cms.Core.PublishedCache
         /// <remarks>If <paramref name="previewToken"/> is null, the snapshot is not previewing, else it
         /// is previewing, and what is or is not visible in preview depends on the content of the token,
         /// which is not specified and depends on the actual published snapshot service implementation.</remarks>
-        IPublishedSnapshot CreatePublishedSnapshot(string previewToken);
+        IPublishedSnapshot CreatePublishedSnapshot(string? previewToken);
 
         /// <summary>
         /// Rebuilds internal database caches (but does not reload).
diff --git a/src/Umbraco.Core/PublishedCache/Internal/InternalPublishedSnapshotService.cs b/src/Umbraco.Core/PublishedCache/Internal/InternalPublishedSnapshotService.cs
index cc080a0f44..bbf121b457 100644
--- a/src/Umbraco.Core/PublishedCache/Internal/InternalPublishedSnapshotService.cs
+++ b/src/Umbraco.Core/PublishedCache/Internal/InternalPublishedSnapshotService.cs
@@ -15,7 +15,7 @@ namespace Umbraco.Cms.Core.PublishedCache.Internal
 
         public Task CollectAsync() => Task.CompletedTask;
 
-        public IPublishedSnapshot CreatePublishedSnapshot(string previewToken)
+        public IPublishedSnapshot CreatePublishedSnapshot(string? previewToken)
         {
             if (previewToken.IsNullOrWhiteSpace())
             {
diff --git a/src/Umbraco.Core/Routing/DomainUtilities.cs b/src/Umbraco.Core/Routing/DomainUtilities.cs
index c754fd6bb4..61b27c3723 100644
--- a/src/Umbraco.Core/Routing/DomainUtilities.cs
+++ b/src/Umbraco.Core/Routing/DomainUtilities.cs
@@ -29,7 +29,7 @@ namespace Umbraco.Cms.Core.Routing
         /// one document per culture), and domains, withing the context of a current Uri, assign
         /// a culture to that document.</para>
         /// </remarks>
-        public static string? GetCultureFromDomains(int contentId, string contentPath, Uri current, IUmbracoContext umbracoContext, ISiteDomainMapper siteDomainMapper)
+        public static string? GetCultureFromDomains(int contentId, string contentPath, Uri? current, IUmbracoContext umbracoContext, ISiteDomainMapper siteDomainMapper)
         {
             if (umbracoContext == null)
                 throw new InvalidOperationException("A current UmbracoContext is required.");
@@ -51,11 +51,11 @@ namespace Umbraco.Cms.Core.Routing
                 : DomainForNode(umbracoContext.Domains, siteDomainMapper, int.Parse(route.Substring(0, pos), CultureInfo.InvariantCulture), current);
 
             var rootContentId = domain?.ContentId ?? -1;
-            var wcDomain = FindWildcardDomainInPath(umbracoContext.Domains.GetAll(true), contentPath, rootContentId);
+            var wcDomain = FindWildcardDomainInPath(umbracoContext.Domains?.GetAll(true), contentPath, rootContentId);
 
             if (wcDomain != null) return wcDomain.Culture;
             if (domain != null) return domain.Culture;
-            return umbracoContext.Domains.DefaultCulture;
+            return umbracoContext.Domains?.DefaultCulture;
         }
 
         #endregion
diff --git a/src/Umbraco.Core/Routing/IPublishedRequestBuilder.cs b/src/Umbraco.Core/Routing/IPublishedRequestBuilder.cs
index 44054a7ab4..e5a915d682 100644
--- a/src/Umbraco.Core/Routing/IPublishedRequestBuilder.cs
+++ b/src/Umbraco.Core/Routing/IPublishedRequestBuilder.cs
@@ -69,7 +69,7 @@ namespace Umbraco.Cms.Core.Routing
         /// <summary>
         /// Sets the culture for the request
         /// </summary>
-        IPublishedRequestBuilder SetCulture(string culture);
+        IPublishedRequestBuilder SetCulture(string? culture);
 
         /// <summary>
         /// Sets the found <see cref="IPublishedContent"/> for the request
diff --git a/src/Umbraco.Core/Routing/PublishedRequestBuilder.cs b/src/Umbraco.Core/Routing/PublishedRequestBuilder.cs
index 6ed63d506c..128c81f605 100644
--- a/src/Umbraco.Core/Routing/PublishedRequestBuilder.cs
+++ b/src/Umbraco.Core/Routing/PublishedRequestBuilder.cs
@@ -94,7 +94,7 @@ namespace Umbraco.Cms.Core.Routing
         }
 
         /// <inheritdoc/>
-        public IPublishedRequestBuilder SetCulture(string culture)
+        public IPublishedRequestBuilder SetCulture(string? culture)
         {
             Culture = culture;
             return this;
diff --git a/src/Umbraco.Core/Security/IBackofficeSecurity.cs b/src/Umbraco.Core/Security/IBackofficeSecurity.cs
index 3bfcd8e1ee..3b3c956cd6 100644
--- a/src/Umbraco.Core/Security/IBackofficeSecurity.cs
+++ b/src/Umbraco.Core/Security/IBackofficeSecurity.cs
@@ -13,7 +13,7 @@ namespace Umbraco.Cms.Core.Security
         // needed in most cases. Where an IUser is required this could be an ext method on the ClaimsIdentity/ClaimsPrincipal that passes in
         // an IUserService, like HttpContext.User.GetUmbracoUser(_userService);
         // This one isn't as easy to remove as the others below.
-        IUser CurrentUser { get; }
+        IUser? CurrentUser { get; }
 
         /// <summary>
         /// Gets the current user's id.
diff --git a/src/Umbraco.Core/Security/IBackofficeSecurityAccessor.cs b/src/Umbraco.Core/Security/IBackofficeSecurityAccessor.cs
index 2999ceacf4..7ef33ecdc6 100644
--- a/src/Umbraco.Core/Security/IBackofficeSecurityAccessor.cs
+++ b/src/Umbraco.Core/Security/IBackofficeSecurityAccessor.cs
@@ -2,6 +2,6 @@ namespace Umbraco.Cms.Core.Security
 {
     public interface IBackOfficeSecurityAccessor
     {
-        IBackOfficeSecurity BackOfficeSecurity { get; }
+        IBackOfficeSecurity? BackOfficeSecurity { get; }
     }
 }
diff --git a/src/Umbraco.Core/Templates/IUmbracoComponentRenderer.cs b/src/Umbraco.Core/Templates/IUmbracoComponentRenderer.cs
index f67ab0a729..bf521d7c6b 100644
--- a/src/Umbraco.Core/Templates/IUmbracoComponentRenderer.cs
+++ b/src/Umbraco.Core/Templates/IUmbracoComponentRenderer.cs
@@ -38,7 +38,7 @@ namespace Umbraco.Cms.Core.Templates
         /// <param name="contentId">The content id</param>
         /// <param name="alias">The alias.</param>
         /// <param name="parameters">The parameters.</param>
-        Task<IHtmlEncodedString> RenderMacroAsync(int contentId, string alias, IDictionary<string, object> parameters);
+        Task<IHtmlEncodedString> RenderMacroAsync(int contentId, string alias, IDictionary<string, object>? parameters);
 
         /// <summary>
         /// Renders the macro with the specified alias, passing in the specified parameters.
diff --git a/src/Umbraco.Core/Templates/UmbracoComponentRenderer.cs b/src/Umbraco.Core/Templates/UmbracoComponentRenderer.cs
index 16f7a609c3..4aee8036a3 100644
--- a/src/Umbraco.Core/Templates/UmbracoComponentRenderer.cs
+++ b/src/Umbraco.Core/Templates/UmbracoComponentRenderer.cs
@@ -60,7 +60,7 @@ namespace Umbraco.Cms.Core.Templates
         public async Task<IHtmlEncodedString> RenderMacroAsync(int contentId, string alias, object parameters) => await RenderMacroAsync(contentId, alias, parameters.ToDictionary<object>());
 
         /// <inheritdoc/>
-        public async Task<IHtmlEncodedString> RenderMacroAsync(int contentId, string alias, IDictionary<string, object> parameters)
+        public async Task<IHtmlEncodedString> RenderMacroAsync(int contentId, string alias, IDictionary<string, object>? parameters)
         {
             if (contentId == default)
             {
@@ -91,7 +91,7 @@ namespace Umbraco.Cms.Core.Templates
         /// <summary>
         /// Renders the macro with the specified alias, passing in the specified parameters.
         /// </summary>
-        private async Task<IHtmlEncodedString> RenderMacroAsync(IPublishedContent content, string alias, IDictionary<string, object> parameters)
+        private async Task<IHtmlEncodedString> RenderMacroAsync(IPublishedContent content, string alias, IDictionary<string, object>? parameters)
         {
             if (content == null)
             {
diff --git a/src/Umbraco.Core/Udi.cs b/src/Umbraco.Core/Udi.cs
index c18bed7a90..2e141e2e66 100644
--- a/src/Umbraco.Core/Udi.cs
+++ b/src/Umbraco.Core/Udi.cs
@@ -91,9 +91,9 @@ namespace Umbraco.Cms.Core
         /// <param name="entityType">The entity type.</param>
         /// <param name="id">The identifier.</param>
         /// <returns>The Guid Udi for the entity type and identifier.</returns>
-        public static Udi Create(string entityType, Guid id)
+        public static Udi Create(string? entityType, Guid id)
         {
-            if (UdiParser.UdiTypes.TryGetValue(entityType, out var udiType) == false)
+            if (entityType is null || UdiParser.UdiTypes.TryGetValue(entityType, out var udiType) == false)
                 throw new ArgumentException(string.Format("Unknown entity type \"{0}\".", entityType), "entityType");
 
             if (udiType != UdiType.GuidUdi)
diff --git a/src/Umbraco.Core/Web/CookieManagerExtensions.cs b/src/Umbraco.Core/Web/CookieManagerExtensions.cs
index d8c4396ab8..75014000bb 100644
--- a/src/Umbraco.Core/Web/CookieManagerExtensions.cs
+++ b/src/Umbraco.Core/Web/CookieManagerExtensions.cs
@@ -8,7 +8,7 @@ namespace Umbraco.Extensions
 {
     public static class CookieManagerExtensions
     {
-        public static string GetPreviewCookieValue(this ICookieManager cookieManager)
+        public static string? GetPreviewCookieValue(this ICookieManager cookieManager)
         {
             return cookieManager.GetCookieValue(Constants.Web.PreviewCookieName);
         }
diff --git a/src/Umbraco.Core/Web/ICookieManager.cs b/src/Umbraco.Core/Web/ICookieManager.cs
index 50a71bf135..730b78a705 100644
--- a/src/Umbraco.Core/Web/ICookieManager.cs
+++ b/src/Umbraco.Core/Web/ICookieManager.cs
@@ -4,7 +4,7 @@ namespace Umbraco.Cms.Core.Web
     public interface ICookieManager
     {
         void ExpireCookie(string cookieName);
-        string GetCookieValue(string cookieName);
+        string? GetCookieValue(string cookieName);
         void SetCookieValue(string cookieName, string value);
         bool HasCookie(string cookieName);
     }
diff --git a/src/Umbraco.Core/Web/IRequestAccessor.cs b/src/Umbraco.Core/Web/IRequestAccessor.cs
index 992b56b75c..9fb4e99d5c 100644
--- a/src/Umbraco.Core/Web/IRequestAccessor.cs
+++ b/src/Umbraco.Core/Web/IRequestAccessor.cs
@@ -17,6 +17,6 @@ namespace Umbraco.Cms.Core.Web
         /// <summary>
         /// Returns the current request uri
         /// </summary>
-        Uri GetRequestUrl();
+        Uri? GetRequestUrl();
     }
 }
diff --git a/src/Umbraco.Core/Web/ISessionManager.cs b/src/Umbraco.Core/Web/ISessionManager.cs
index f2bc0136d0..bd0cab9cd6 100644
--- a/src/Umbraco.Core/Web/ISessionManager.cs
+++ b/src/Umbraco.Core/Web/ISessionManager.cs
@@ -2,7 +2,7 @@ namespace Umbraco.Cms.Core.Web
 {
     public interface ISessionManager
     {
-        string GetSessionValue(string sessionName);
+        string? GetSessionValue(string sessionName);
         void SetSessionValue(string sessionName, string value);
     }
 }
diff --git a/src/Umbraco.Core/Web/IUmbracoContext.cs b/src/Umbraco.Core/Web/IUmbracoContext.cs
index a7b2402901..d591d23e70 100644
--- a/src/Umbraco.Core/Web/IUmbracoContext.cs
+++ b/src/Umbraco.Core/Web/IUmbracoContext.cs
@@ -45,14 +45,14 @@ namespace Umbraco.Cms.Core.Web
         /// <summary>
         /// Gets the domains cache.
         /// </summary>
-        IDomainCache Domains { get; }
+        IDomainCache? Domains { get; }
 
         /// <summary>
         /// Gets or sets the PublishedRequest object
         /// </summary>
         //// TODO: Can we refactor this so it's not a settable thing required for routing?
         //// The only nicer way would be to have a RouteRequest method directly on IUmbracoContext but that means adding another dep to the ctx/factory.
-        IPublishedRequest PublishedRequest { get; set; }
+        IPublishedRequest? PublishedRequest { get; set; }
 
         /// <summary>
         /// Gets a value indicating whether the request has debugging enabled
diff --git a/src/Umbraco.Infrastructure/DependencyInjection/UmbracoBuilder.Collections.cs b/src/Umbraco.Infrastructure/DependencyInjection/UmbracoBuilder.Collections.cs
index c63094821c..7091b89cad 100644
--- a/src/Umbraco.Infrastructure/DependencyInjection/UmbracoBuilder.Collections.cs
+++ b/src/Umbraco.Infrastructure/DependencyInjection/UmbracoBuilder.Collections.cs
@@ -14,10 +14,10 @@ namespace Umbraco.Extensions
         /// Gets the mappers collection builder.
         /// </summary>
         /// <param name="builder">The builder.</param>
-        public static MapperCollectionBuilder Mappers(this IUmbracoBuilder builder)
+        public static MapperCollectionBuilder? Mappers(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<MapperCollectionBuilder>();
 
-        public static NPocoMapperCollectionBuilder NPocoMappers(this IUmbracoBuilder builder)
+        public static NPocoMapperCollectionBuilder? NPocoMappers(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<NPocoMapperCollectionBuilder>();
 
 
@@ -25,7 +25,7 @@ namespace Umbraco.Extensions
         /// Gets the package migration plans collection builder.
         /// </summary>
         /// <param name="builder">The builder.</param>
-        public static PackageMigrationPlanCollectionBuilder PackageMigrationPlans(this IUmbracoBuilder builder)
+        public static PackageMigrationPlanCollectionBuilder? PackageMigrationPlans(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<PackageMigrationPlanCollectionBuilder>();
 
     }
diff --git a/src/Umbraco.Infrastructure/DependencyInjection/UmbracoBuilder.CoreServices.cs b/src/Umbraco.Infrastructure/DependencyInjection/UmbracoBuilder.CoreServices.cs
index 17ca813b3f..0c8b8c3343 100644
--- a/src/Umbraco.Infrastructure/DependencyInjection/UmbracoBuilder.CoreServices.cs
+++ b/src/Umbraco.Infrastructure/DependencyInjection/UmbracoBuilder.CoreServices.cs
@@ -73,8 +73,8 @@ namespace Umbraco.Cms.Infrastructure.DependencyInjection
             builder.Services.AddSingleton<IDistributedLockingMechanismFactory, DefaultDistributedLockingMechanismFactory>();
             builder.Services.AddSingleton<IUmbracoDatabaseFactory, UmbracoDatabaseFactory>();
             builder.Services.AddSingleton(factory => factory.GetRequiredService<IUmbracoDatabaseFactory>().SqlContext);
-            builder.NPocoMappers().Add<NullableDateMapper>();
-            builder.PackageMigrationPlans().Add(() => builder.TypeLoader.GetPackageMigrationPlans());
+            builder.NPocoMappers()?.Add<NullableDateMapper>();
+            builder.PackageMigrationPlans()?.Add(() => builder.TypeLoader.GetPackageMigrationPlans());
 
             builder.Services.AddSingleton<IRuntimeState, RuntimeState>();
             builder.Services.AddSingleton<IRuntime, CoreRuntime>();
@@ -93,7 +93,7 @@ namespace Umbraco.Cms.Infrastructure.DependencyInjection
             // register persistence mappers - required by database factory so needs to be done here
             // means the only place the collection can be modified is in a runtime - afterwards it
             // has been frozen and it is too late
-            builder.Mappers().AddCoreMappers();
+            builder.Mappers()?.AddCoreMappers();
 
             // register the scope provider
             builder.Services.AddSingleton<ScopeProvider>(); // implements IScopeProvider, IScopeAccessor
@@ -117,7 +117,7 @@ namespace Umbraco.Cms.Infrastructure.DependencyInjection
             // register the manifest filter collection builder (collection is empty by default)
             builder.ManifestFilters();
 
-            builder.MediaUrlGenerators()
+            builder.MediaUrlGenerators()?
                 .Add<FileUploadPropertyEditor>()
                 .Add<ImageCropperPropertyEditor>();
 
@@ -147,7 +147,7 @@ namespace Umbraco.Cms.Infrastructure.DependencyInjection
             // both TinyMceValueConverter (in Core) and RteMacroRenderingValueConverter (in Web) will be
             // discovered when CoreBootManager configures the converters. We will remove the basic one defined
             // in core so that the more enhanced version is active.
-            builder.PropertyValueConverters()
+            builder.PropertyValueConverters()?
                 .Remove<SimpleTinyMceValueConverter>();
 
             // register *all* checks, except those marked [HideFromTypeFinder] of course
@@ -263,7 +263,7 @@ namespace Umbraco.Cms.Infrastructure.DependencyInjection
 
         private static IUmbracoBuilder AddPreValueMigrators(this IUmbracoBuilder builder)
         {
-            builder.WithCollectionBuilder<PreValueMigratorCollectionBuilder>()
+            builder.WithCollectionBuilder<PreValueMigratorCollectionBuilder>()?
                 .Append<RenamingPreValueMigrator>()
                 .Append<RichTextPreValueMigrator>()
                 .Append<UmbracoSliderPreValueMigrator>()
diff --git a/src/Umbraco.Infrastructure/DependencyInjection/UmbracoBuilder.MappingProfiles.cs b/src/Umbraco.Infrastructure/DependencyInjection/UmbracoBuilder.MappingProfiles.cs
index 42ce7f7932..e1d58a32eb 100644
--- a/src/Umbraco.Infrastructure/DependencyInjection/UmbracoBuilder.MappingProfiles.cs
+++ b/src/Umbraco.Infrastructure/DependencyInjection/UmbracoBuilder.MappingProfiles.cs
@@ -16,7 +16,7 @@ namespace Umbraco.Cms.Infrastructure.DependencyInjection
         {
             builder.Services.AddUnique<IUmbracoMapper, UmbracoMapper>();
 
-            builder.WithCollectionBuilder<MapDefinitionCollectionBuilder>()
+            builder.WithCollectionBuilder<MapDefinitionCollectionBuilder>()?
                 .Add<AuditMapDefinition>()
                 .Add<CodeFileMapDefinition>()
                 .Add<ContentPropertyMapDefinition>()
diff --git a/src/Umbraco.Infrastructure/PropertyEditors/ValueConverters/ImageCropperValue.cs b/src/Umbraco.Infrastructure/PropertyEditors/ValueConverters/ImageCropperValue.cs
index 0ee35852a2..a8e1360920 100644
--- a/src/Umbraco.Infrastructure/PropertyEditors/ValueConverters/ImageCropperValue.cs
+++ b/src/Umbraco.Infrastructure/PropertyEditors/ValueConverters/ImageCropperValue.cs
@@ -52,7 +52,7 @@ namespace Umbraco.Cms.Core.PropertyEditors.ValueConverters
         /// <summary>
         /// Gets a crop.
         /// </summary>
-        public ImageCropperCrop? GetCrop(string alias)
+        public ImageCropperCrop? GetCrop(string? alias)
         {
             if (Crops == null)
                 return null;
@@ -228,7 +228,7 @@ namespace Umbraco.Cms.Core.PropertyEditors.ValueConverters
         public override bool Equals(object? obj)
             => ReferenceEquals(this, obj) || obj is ImageCropperValue other && Equals(this, other);
 
-        private static bool Equals(ImageCropperValue left, ImageCropperValue? right)
+        private static bool Equals(ImageCropperValue? left, ImageCropperValue? right)
             => ReferenceEquals(left, right) // deals with both being null, too
                 || !ReferenceEquals(left, null) && !ReferenceEquals(right, null)
                    && string.Equals(left.Src, right.Src)
@@ -238,10 +238,10 @@ namespace Umbraco.Cms.Core.PropertyEditors.ValueConverters
         private IEnumerable<ImageCropperCrop> ComparableCrops
             => Crops?.OrderBy(x => x.Alias) ?? Enumerable.Empty<ImageCropperCrop>();
 
-        public static bool operator ==(ImageCropperValue left, ImageCropperValue right)
+        public static bool operator ==(ImageCropperValue? left, ImageCropperValue? right)
             => Equals(left, right);
 
-        public static bool operator !=(ImageCropperValue left, ImageCropperValue right)
+        public static bool operator !=(ImageCropperValue? left, ImageCropperValue? right)
             => !Equals(left, right);
 
         public override int GetHashCode()
@@ -330,7 +330,7 @@ namespace Umbraco.Cms.Core.PropertyEditors.ValueConverters
             public override bool Equals(object? obj)
                 => ReferenceEquals(this, obj) || obj is ImageCropperCrop other && Equals(this, other);
 
-            private static bool Equals(ImageCropperCrop left, ImageCropperCrop? right)
+            private static bool Equals(ImageCropperCrop? left, ImageCropperCrop? right)
                 => ReferenceEquals(left, right) // deals with both being null, too
                     || !ReferenceEquals(left, null) && !ReferenceEquals(right, null)
                        && string.Equals(left.Alias, right.Alias)
@@ -338,10 +338,10 @@ namespace Umbraco.Cms.Core.PropertyEditors.ValueConverters
                        && left.Height == right.Height
                        && Equals(left.Coordinates, right.Coordinates);
 
-            public static bool operator ==(ImageCropperCrop left, ImageCropperCrop right)
+            public static bool operator ==(ImageCropperCrop? left, ImageCropperCrop? right)
                 => Equals(left, right);
 
-            public static bool operator !=(ImageCropperCrop left, ImageCropperCrop right)
+            public static bool operator !=(ImageCropperCrop? left, ImageCropperCrop? right)
                 => !Equals(left, right);
 
             public override int GetHashCode()
@@ -387,7 +387,7 @@ namespace Umbraco.Cms.Core.PropertyEditors.ValueConverters
             public override bool Equals(object? obj)
                 => ReferenceEquals(this, obj) || obj is ImageCropperCropCoordinates other && Equals(this, other);
 
-            private static bool Equals(ImageCropperCropCoordinates left, ImageCropperCropCoordinates? right)
+            private static bool Equals(ImageCropperCropCoordinates? left, ImageCropperCropCoordinates? right)
                 => ReferenceEquals(left, right) // deals with both being null, too
                    || !ReferenceEquals(left, null) && !ReferenceEquals(right, null)
                       && left.X1 == right.X1
@@ -395,7 +395,7 @@ namespace Umbraco.Cms.Core.PropertyEditors.ValueConverters
                       && left.Y1 == right.Y1
                       && left.Y2 == right.Y2;
 
-            public static bool operator ==(ImageCropperCropCoordinates left, ImageCropperCropCoordinates right)
+            public static bool operator ==(ImageCropperCropCoordinates? left, ImageCropperCropCoordinates? right)
                 => Equals(left, right);
 
             public static bool operator !=(ImageCropperCropCoordinates left, ImageCropperCropCoordinates right)
diff --git a/src/Umbraco.Infrastructure/Security/IMemberManager.cs b/src/Umbraco.Infrastructure/Security/IMemberManager.cs
index d7558e163f..d9c636e2f7 100644
--- a/src/Umbraco.Infrastructure/Security/IMemberManager.cs
+++ b/src/Umbraco.Infrastructure/Security/IMemberManager.cs
@@ -14,13 +14,13 @@ namespace Umbraco.Cms.Core.Security
         /// </summary>
         /// <param name="user"></param>
         /// <returns></returns>
-        IPublishedContent AsPublishedMember(MemberIdentityUser user);
+        IPublishedContent? AsPublishedMember(MemberIdentityUser user);
 
         /// <summary>
         /// Returns the currently logged in member if there is one, else returns null
         /// </summary>
         /// <returns></returns>
-        Task<MemberIdentityUser> GetCurrentMemberAsync();
+        Task<MemberIdentityUser?> GetCurrentMemberAsync();
 
         /// <summary>
         /// Checks if the current member is authorized based on the parameters provided.
diff --git a/src/Umbraco.PublishedCache.NuCache/PublishedSnapshotService.cs b/src/Umbraco.PublishedCache.NuCache/PublishedSnapshotService.cs
index 20df726080..80dfc8b73d 100644
--- a/src/Umbraco.PublishedCache.NuCache/PublishedSnapshotService.cs
+++ b/src/Umbraco.PublishedCache.NuCache/PublishedSnapshotService.cs
@@ -974,7 +974,7 @@ namespace Umbraco.Cms.Infrastructure.PublishedCache
             }
         }
 
-        public IPublishedSnapshot CreatePublishedSnapshot(string previewToken)
+        public IPublishedSnapshot CreatePublishedSnapshot(string? previewToken)
         {
             EnsureCaches();
 
diff --git a/src/Umbraco.Web.Common/ActionsResults/PublishedContentNotFoundResult.cs b/src/Umbraco.Web.Common/ActionsResults/PublishedContentNotFoundResult.cs
index 0eb30bcd03..417ed622bd 100644
--- a/src/Umbraco.Web.Common/ActionsResults/PublishedContentNotFoundResult.cs
+++ b/src/Umbraco.Web.Common/ActionsResults/PublishedContentNotFoundResult.cs
@@ -13,12 +13,12 @@ namespace Umbraco.Cms.Web.Common.ActionsResults
     public class PublishedContentNotFoundResult : IActionResult
     {
         private readonly IUmbracoContext _umbracoContext;
-        private readonly string _message;
+        private readonly string? _message;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="PublishedContentNotFoundResult"/> class.
         /// </summary>
-        public PublishedContentNotFoundResult(IUmbracoContext umbracoContext, string message = null)
+        public PublishedContentNotFoundResult(IUmbracoContext umbracoContext, string? message = null)
         {
             _umbracoContext = umbracoContext;
             _message = message;
@@ -33,13 +33,13 @@ namespace Umbraco.Cms.Web.Common.ActionsResults
 
             response.StatusCode = StatusCodes.Status404NotFound;
 
-            IPublishedRequest frequest = _umbracoContext.PublishedRequest;
+            IPublishedRequest? frequest = _umbracoContext.PublishedRequest;
             var reason = "Cannot render the page at URL '{0}'.";
-            if (frequest.HasPublishedContent() == false)
+            if (frequest?.HasPublishedContent() == false)
             {
                 reason = "No umbraco document matches the URL '{0}'.";
             }
-            else if (frequest.HasTemplate() == false)
+            else if (frequest?.HasTemplate() == false)
             {
                 reason = "No template exists to render the document at URL '{0}'.";
             }
diff --git a/src/Umbraco.Web.Common/ApplicationBuilder/UmbracoApplicationBuilder.cs b/src/Umbraco.Web.Common/ApplicationBuilder/UmbracoApplicationBuilder.cs
index 58f66a6fb8..fc9780016b 100644
--- a/src/Umbraco.Web.Common/ApplicationBuilder/UmbracoApplicationBuilder.cs
+++ b/src/Umbraco.Web.Common/ApplicationBuilder/UmbracoApplicationBuilder.cs
@@ -99,15 +99,18 @@ namespace Umbraco.Cms.Web.Common.ApplicationBuilder
 
             // Get media file provider and request path/URL
             var mediaFileManager = AppBuilder.ApplicationServices.GetRequiredService<MediaFileManager>();
-            if (mediaFileManager.FileSystem.TryCreateFileProvider(out IFileProvider mediaFileProvider))
+            if (mediaFileManager.FileSystem.TryCreateFileProvider(out IFileProvider? mediaFileProvider))
             {
                 GlobalSettings globalSettings = AppBuilder.ApplicationServices.GetRequiredService<IOptions<GlobalSettings>>().Value;
-                IHostingEnvironment hostingEnvironment = AppBuilder.ApplicationServices.GetService<IHostingEnvironment>();
-                string mediaRequestPath = hostingEnvironment.ToAbsolute(globalSettings.UmbracoMediaPath);
+                IHostingEnvironment? hostingEnvironment = AppBuilder.ApplicationServices.GetService<IHostingEnvironment>();
+                string? mediaRequestPath = hostingEnvironment?.ToAbsolute(globalSettings.UmbracoMediaPath);
 
                 // Configure custom file provider for media
-                IWebHostEnvironment webHostEnvironment = AppBuilder.ApplicationServices.GetService<IWebHostEnvironment>();
-                webHostEnvironment.WebRootFileProvider = webHostEnvironment.WebRootFileProvider.ConcatComposite(new PrependBasePathFileProvider(mediaRequestPath, mediaFileProvider));
+                IWebHostEnvironment? webHostEnvironment = AppBuilder.ApplicationServices.GetService<IWebHostEnvironment>();
+                if (webHostEnvironment is not null)
+                {
+                    webHostEnvironment.WebRootFileProvider = webHostEnvironment.WebRootFileProvider.ConcatComposite(new PrependBasePathFileProvider(mediaRequestPath, mediaFileProvider));
+                }
             }
 
             AppBuilder.UseStaticFiles();
diff --git a/src/Umbraco.Web.Common/ApplicationBuilder/UmbracoPipelineFilter.cs b/src/Umbraco.Web.Common/ApplicationBuilder/UmbracoPipelineFilter.cs
index 625cfc41d8..25d006634a 100644
--- a/src/Umbraco.Web.Common/ApplicationBuilder/UmbracoPipelineFilter.cs
+++ b/src/Umbraco.Web.Common/ApplicationBuilder/UmbracoPipelineFilter.cs
@@ -15,9 +15,9 @@ namespace Umbraco.Cms.Web.Common.ApplicationBuilder
 
         public UmbracoPipelineFilter(
             string name,
-            Action<IApplicationBuilder> prePipeline,
-            Action<IApplicationBuilder> postPipeline,
-            Action<IApplicationBuilder> endpointCallback)
+            Action<IApplicationBuilder>? prePipeline,
+            Action<IApplicationBuilder>? postPipeline,
+            Action<IApplicationBuilder>? endpointCallback)
         {
             Name = name ?? throw new ArgumentNullException(nameof(name));
             PrePipeline = prePipeline;
@@ -25,9 +25,9 @@ namespace Umbraco.Cms.Web.Common.ApplicationBuilder
             Endpoints = endpointCallback;
         }
 
-        public Action<IApplicationBuilder> PrePipeline { get; set; }
-        public Action<IApplicationBuilder> PostPipeline { get; set; }
-        public Action<IApplicationBuilder> Endpoints { get; set; }
+        public Action<IApplicationBuilder>? PrePipeline { get; set; }
+        public Action<IApplicationBuilder>? PostPipeline { get; set; }
+        public Action<IApplicationBuilder>? Endpoints { get; set; }
         public string Name { get; }
 
         public void OnPrePipeline(IApplicationBuilder app) => PrePipeline?.Invoke(app);
diff --git a/src/Umbraco.Web.Common/AspNetCore/AspNetCoreBackOfficeInfo.cs b/src/Umbraco.Web.Common/AspNetCore/AspNetCoreBackOfficeInfo.cs
index f006fb03f4..7107ab3331 100644
--- a/src/Umbraco.Web.Common/AspNetCore/AspNetCoreBackOfficeInfo.cs
+++ b/src/Umbraco.Web.Common/AspNetCore/AspNetCoreBackOfficeInfo.cs
@@ -11,7 +11,7 @@ namespace Umbraco.Cms.Web.Common.AspNetCore
     {
         private readonly IOptionsMonitor<GlobalSettings> _globalSettings;
         private readonly IHostingEnvironment _hostingEnvironment;
-        private string _getAbsoluteUrl;
+        private string? _getAbsoluteUrl;
         public AspNetCoreBackOfficeInfo(IOptionsMonitor<GlobalSettings> globalSettings, IHostingEnvironment hostingEnviroment)
         {
             _globalSettings = globalSettings;
diff --git a/src/Umbraco.Web.Common/AspNetCore/AspNetCoreCookieManager.cs b/src/Umbraco.Web.Common/AspNetCore/AspNetCoreCookieManager.cs
index 1ba86eac0c..478e8aa13d 100644
--- a/src/Umbraco.Web.Common/AspNetCore/AspNetCoreCookieManager.cs
+++ b/src/Umbraco.Web.Common/AspNetCore/AspNetCoreCookieManager.cs
@@ -27,7 +27,7 @@ namespace Umbraco.Cms.Web.Common.AspNetCore
             });
         }
 
-        public string GetCookieValue(string cookieName)
+        public string? GetCookieValue(string cookieName)
         {
             return _httpContextAccessor.HttpContext?.Request.Cookies[cookieName];
         }
diff --git a/src/Umbraco.Web.Common/AspNetCore/AspNetCoreHostingEnvironment.cs b/src/Umbraco.Web.Common/AspNetCore/AspNetCoreHostingEnvironment.cs
index 13f73e1b41..d672f2ae1c 100644
--- a/src/Umbraco.Web.Common/AspNetCore/AspNetCoreHostingEnvironment.cs
+++ b/src/Umbraco.Web.Common/AspNetCore/AspNetCoreHostingEnvironment.cs
@@ -21,8 +21,8 @@ namespace Umbraco.Cms.Web.Common.AspNetCore
         private readonly IOptionsMonitor<HostingSettings> _hostingSettings;
         private readonly IOptionsMonitor<WebRoutingSettings> _webRoutingSettings;
         private readonly IWebHostEnvironment _webHostEnvironment;
-        private string _applicationId;
-        private string _localTempPath;
+        private string? _applicationId;
+        private string? _localTempPath;
         private UrlMode _urlProviderMode;
 
         public AspNetCoreHostingEnvironment(
@@ -59,10 +59,10 @@ namespace Umbraco.Cms.Web.Common.AspNetCore
         public bool IsHosted { get; } = true;
 
         /// <inheritdoc/>
-        public Uri ApplicationMainUrl { get; private set; }
+        public Uri ApplicationMainUrl { get; private set; } = null!;
 
         /// <inheritdoc/>
-        public string SiteName { get; private set; }
+        public string SiteName { get; private set; } = null!;
 
         /// <inheritdoc/>
         public string ApplicationId
@@ -98,7 +98,7 @@ namespace Umbraco.Cms.Web.Common.AspNetCore
         /// <inheritdoc/>
         public bool IsDebugMode => _hostingSettings.CurrentValue.Debug;
 
-        public Version IISVersion { get; }
+        public Version? IISVersion { get; }
 
         public string LocalTempPath
         {
@@ -177,7 +177,7 @@ namespace Umbraco.Cms.Web.Common.AspNetCore
             return fullPath;
         }
 
-        public void EnsureApplicationMainUrl(Uri currentApplicationUrl)
+        public void EnsureApplicationMainUrl(Uri? currentApplicationUrl)
         {
             // Fixme: This causes problems with site swap on azure because azure pre-warms a site by calling into `localhost` and when it does that
             // it changes the URL to `localhost:80` which actually doesn't work for pinging itself, it only works internally in Azure. The ironic part
@@ -208,7 +208,7 @@ namespace Umbraco.Cms.Web.Common.AspNetCore
             }
         }
 
-        private void SetSiteName(string siteName) =>
+        private void SetSiteName(string? siteName) =>
             SiteName = string.IsNullOrWhiteSpace(siteName)
                 ? _webHostEnvironment.ApplicationName
                 : siteName;
diff --git a/src/Umbraco.Web.Common/AspNetCore/AspNetCorePasswordHasher.cs b/src/Umbraco.Web.Common/AspNetCore/AspNetCorePasswordHasher.cs
index a68b27ec86..17c1306789 100644
--- a/src/Umbraco.Web.Common/AspNetCore/AspNetCorePasswordHasher.cs
+++ b/src/Umbraco.Web.Common/AspNetCore/AspNetCorePasswordHasher.cs
@@ -13,7 +13,7 @@ namespace Umbraco.Cms.Web.Common.AspNetCore
 
         public string HashPassword(string password)
         {
-            return _underlyingHasher.HashPassword(null, password);
+            return _underlyingHasher.HashPassword(null!, password);
         }
     }
 }
diff --git a/src/Umbraco.Web.Common/AspNetCore/AspNetCoreRequestAccessor.cs b/src/Umbraco.Web.Common/AspNetCore/AspNetCoreRequestAccessor.cs
index d140b848c8..9924ae9109 100644
--- a/src/Umbraco.Web.Common/AspNetCore/AspNetCoreRequestAccessor.cs
+++ b/src/Umbraco.Web.Common/AspNetCore/AspNetCoreRequestAccessor.cs
@@ -17,7 +17,7 @@ namespace Umbraco.Cms.Web.Common.AspNetCore
         private readonly IHttpContextAccessor _httpContextAccessor;
         private WebRoutingSettings _webRoutingSettings;
         private readonly ISet<string> _applicationUrls = new HashSet<string>();
-        private Uri _currentApplicationUrl;
+        private Uri? _currentApplicationUrl;
         private object _initLocker = new object();
         private bool _hasAppUrl = false;
         private bool _isInit = false;
@@ -38,7 +38,7 @@ namespace Umbraco.Cms.Web.Common.AspNetCore
         /// <inheritdoc/>
         public string GetRequestValue(string name) => GetFormValue(name) ?? GetQueryStringValue(name);
 
-        private string GetFormValue(string name)
+        private string? GetFormValue(string name)
         {
             var request = _httpContextAccessor.GetRequiredHttpContext().Request;
             if (!request.HasFormContentType)
@@ -50,10 +50,10 @@ namespace Umbraco.Cms.Web.Common.AspNetCore
         public string GetQueryStringValue(string name) => _httpContextAccessor.GetRequiredHttpContext().Request.Query[name];
 
         /// <inheritdoc/>
-        public Uri GetRequestUrl() => _httpContextAccessor.HttpContext != null ? new Uri(_httpContextAccessor.HttpContext.Request.GetEncodedUrl()) : null;
+        public Uri? GetRequestUrl() => _httpContextAccessor.HttpContext != null ? new Uri(_httpContextAccessor.HttpContext.Request.GetEncodedUrl()) : null;
 
         /// <inheritdoc/>
-        public Uri GetApplicationUrl()
+        public Uri? GetApplicationUrl()
         {
             // Fixme: This causes problems with site swap on azure because azure pre-warms a site by calling into `localhost` and when it does that
             // it changes the URL to `localhost:80` which actually doesn't work for pinging itself, it only works internally in Azure. The ironic part
@@ -76,8 +76,7 @@ namespace Umbraco.Cms.Web.Common.AspNetCore
             }
 
             var url = UriHelper.BuildAbsolute(request.Scheme, request.Host);
-            var change = url != null && !_applicationUrls.Contains(url);
-            if (change)
+            if (url != null && !_applicationUrls.Contains(url))
             {
                 _applicationUrls.Add(url);
 
diff --git a/src/Umbraco.Web.Common/AspNetCore/AspNetCoreSessionManager.cs b/src/Umbraco.Web.Common/AspNetCore/AspNetCoreSessionManager.cs
index 9732d43e2d..a4d4e53a60 100644
--- a/src/Umbraco.Web.Common/AspNetCore/AspNetCoreSessionManager.cs
+++ b/src/Umbraco.Web.Common/AspNetCore/AspNetCoreSessionManager.cs
@@ -20,7 +20,7 @@ namespace Umbraco.Cms.Web.Common.AspNetCore
         /// </summary>
         private bool IsSessionsAvailable => !(_httpContextAccessor.HttpContext?.Features.Get<ISessionFeature>() is null);
 
-        public string SessionId
+        public string? SessionId
         {
             get
             {
@@ -32,7 +32,7 @@ namespace Umbraco.Cms.Web.Common.AspNetCore
             }
         }
 
-        public string GetSessionValue(string sessionName)
+        public string? GetSessionValue(string sessionName)
         {
             if(!IsSessionsAvailable) return null;
             return _httpContextAccessor.HttpContext?.Session.GetString(sessionName);
diff --git a/src/Umbraco.Web.Common/AspNetCore/AspNetCoreUserAgentProvider.cs b/src/Umbraco.Web.Common/AspNetCore/AspNetCoreUserAgentProvider.cs
index 8e94fc3b80..d8d23e32f6 100644
--- a/src/Umbraco.Web.Common/AspNetCore/AspNetCoreUserAgentProvider.cs
+++ b/src/Umbraco.Web.Common/AspNetCore/AspNetCoreUserAgentProvider.cs
@@ -12,9 +12,9 @@ namespace Umbraco.Cms.Web.Common.AspNetCore
             _httpContextAccessor = httpContextAccessor;
         }
 
-        public string GetUserAgent()
+        public string? GetUserAgent()
         {
-            return _httpContextAccessor.HttpContext.Request.Headers["User-Agent"].ToString();
+            return _httpContextAccessor.HttpContext?.Request.Headers["User-Agent"].ToString();
         }
     }
 }
diff --git a/src/Umbraco.Web.Common/Authorization/FeatureAuthorizeHandler.cs b/src/Umbraco.Web.Common/Authorization/FeatureAuthorizeHandler.cs
index 283accb085..bc025d4f06 100644
--- a/src/Umbraco.Web.Common/Authorization/FeatureAuthorizeHandler.cs
+++ b/src/Umbraco.Web.Common/Authorization/FeatureAuthorizeHandler.cs
@@ -42,15 +42,15 @@ namespace Umbraco.Cms.Web.Common.Authorization
             {
                 case DefaultHttpContext defaultHttpContext:
                 {
-                    IEndpointFeature endpointFeature = defaultHttpContext.Features.Get<IEndpointFeature>();
-                    endpoint = endpointFeature.Endpoint;
+                    IEndpointFeature? endpointFeature = defaultHttpContext.Features.Get<IEndpointFeature>();
+                    endpoint = endpointFeature?.Endpoint;
                     break;
                 }
 
                 case Microsoft.AspNetCore.Mvc.Filters.AuthorizationFilterContext authorizationFilterContext:
                 {
-                    IEndpointFeature endpointFeature = authorizationFilterContext.HttpContext.Features.Get<IEndpointFeature>();
-                    endpoint = endpointFeature.Endpoint;
+                    IEndpointFeature? endpointFeature = authorizationFilterContext.HttpContext.Features.Get<IEndpointFeature>();
+                    endpoint = endpointFeature?.Endpoint;
                     break;
                 }
 
@@ -67,7 +67,7 @@ namespace Umbraco.Cms.Web.Common.Authorization
             }
 
             var actionDescriptor = endpoint.Metadata.GetMetadata<ControllerActionDescriptor>();
-            var controllerType = actionDescriptor.ControllerTypeInfo.AsType();
+            var controllerType = actionDescriptor?.ControllerTypeInfo.AsType();
             return _umbracoFeatures.IsControllerEnabled(controllerType);
         }
     }
diff --git a/src/Umbraco.Web.Common/Cache/HttpContextRequestAppCache.cs b/src/Umbraco.Web.Common/Cache/HttpContextRequestAppCache.cs
index 9e384879e3..6f4455dc74 100644
--- a/src/Umbraco.Web.Common/Cache/HttpContextRequestAppCache.cs
+++ b/src/Umbraco.Web.Common/Cache/HttpContextRequestAppCache.cs
@@ -1,6 +1,7 @@
 using System;
 using System.Collections;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Threading;
 using Microsoft.AspNetCore.Http;
@@ -31,14 +32,14 @@ namespace Umbraco.Cms.Core.Cache
 
         public bool IsAvailable => TryGetContextItems(out _);
 
-        private bool TryGetContextItems(out IDictionary<object, object> items)
+        private bool TryGetContextItems([MaybeNullWhen(false)] out IDictionary<object, object?> items)
         {
             items = _httpContextAccessor.HttpContext?.Items;
             return items != null;
         }
 
         /// <inheritdoc />
-        public override object Get(string key, Func<object?> factory)
+        public override object? Get(string key, Func<object?> factory)
         {
             //no place to cache so just return the callback result
             if (!TryGetContextItems(out var items))
@@ -48,12 +49,12 @@ namespace Umbraco.Cms.Core.Cache
 
             key = GetCacheKey(key);
 
-            Lazy<object> result;
+            Lazy<object?>? result;
 
             try
             {
                 EnterWriteLock();
-                result = items[key] as Lazy<object>; // null if key not found
+                result = items[key] as Lazy<object?>; // null if key not found
 
                 // cannot create value within the lock, so if result.IsValueCreated is false, just
                 // do nothing here - means that if creation throws, a race condition could cause
@@ -86,7 +87,7 @@ namespace Umbraco.Cms.Core.Cache
             return value;
         }
 
-        public bool Set(string key, object value)
+        public bool Set(string key, object? value)
         {
             //no place to cache so just return the callback result
             if (!TryGetContextItems(out var items))
@@ -151,7 +152,7 @@ namespace Umbraco.Cms.Core.Cache
             items.Remove(key);
         }
 
-        protected override object GetEntry(string key)
+        protected override object? GetEntry(string key)
         {
             return !TryGetContextItems(out var items) ? null : items[key];
         }
@@ -162,7 +163,7 @@ namespace Umbraco.Cms.Core.Cache
 
         protected override void EnterReadLock()
         {
-            object locker = GetLock();
+            object? locker = GetLock();
             if (locker == null)
             {
                 return;
@@ -172,7 +173,7 @@ namespace Umbraco.Cms.Core.Cache
 
         protected override void EnterWriteLock()
         {
-            object locker = GetLock();
+            object? locker = GetLock();
             if (locker == null)
             {
                 return;
@@ -182,7 +183,7 @@ namespace Umbraco.Cms.Core.Cache
 
         protected override void ExitReadLock()
         {
-            object locker = GetLock();
+            object? locker = GetLock();
             if (locker == null)
             {
                 return;
@@ -195,7 +196,7 @@ namespace Umbraco.Cms.Core.Cache
 
         protected override void ExitWriteLock()
         {
-            object locker = GetLock();
+            object? locker = GetLock();
             if (locker == null)
             {
                 return;
@@ -208,16 +209,16 @@ namespace Umbraco.Cms.Core.Cache
 
         #endregion
 
-        public IEnumerator<KeyValuePair<string, object>> GetEnumerator()
+        public IEnumerator<KeyValuePair<string, object?>> GetEnumerator()
         {
-            if (!TryGetContextItems(out IDictionary<object, object> items))
+            if (!TryGetContextItems(out IDictionary<object, object?>? items))
             {
                 yield break;
             }
 
-            foreach (KeyValuePair<object, object> item in items)
+            foreach (KeyValuePair<object, object?> item in items)
             {
-                yield return new KeyValuePair<string, object>(item.Key.ToString(), item.Value);
+                yield return new KeyValuePair<string, object?>(item.Key.ToString()!, item.Value);
             }
         }
 
@@ -227,15 +228,15 @@ namespace Umbraco.Cms.Core.Cache
         /// Ensures and returns the current lock
         /// </summary>
         /// <returns></returns>
-        private object GetLock()
+        private object? GetLock()
         {
-            HttpContext httpContext = _httpContextAccessor.HttpContext;
+            HttpContext? httpContext = _httpContextAccessor.HttpContext;
             if (httpContext == null)
             {
                 return null;
             }
 
-            RequestLock requestLock = httpContext.Features.Get<RequestLock>();
+            RequestLock? requestLock = httpContext.Features.Get<RequestLock>();
             if (requestLock != null)
             {
                 return requestLock.SyncRoot;
diff --git a/src/Umbraco.Web.Common/Controllers/PublishedRequestFilterAttribute.cs b/src/Umbraco.Web.Common/Controllers/PublishedRequestFilterAttribute.cs
index 0d8c0833e1..4274a1ab16 100644
--- a/src/Umbraco.Web.Common/Controllers/PublishedRequestFilterAttribute.cs
+++ b/src/Umbraco.Web.Common/Controllers/PublishedRequestFilterAttribute.cs
@@ -17,7 +17,7 @@ namespace Umbraco.Cms.Web.Common.Controllers
         /// </summary>
         protected UmbracoRouteValues GetUmbracoRouteValues(ResultExecutingContext context)
         {
-            UmbracoRouteValues routeVals = context.HttpContext.Features.Get<UmbracoRouteValues>();
+            UmbracoRouteValues? routeVals = context.HttpContext.Features.Get<UmbracoRouteValues>();
             if (routeVals == null)
             {
                 throw new InvalidOperationException($"No {nameof(UmbracoRouteValues)} feature was found in the HttpContext");
diff --git a/src/Umbraco.Web.Common/Controllers/RenderController.cs b/src/Umbraco.Web.Common/Controllers/RenderController.cs
index 4d74dd1767..46d3d4119d 100644
--- a/src/Umbraco.Web.Common/Controllers/RenderController.cs
+++ b/src/Umbraco.Web.Common/Controllers/RenderController.cs
@@ -93,8 +93,8 @@ namespace Umbraco.Cms.Web.Common.Controllers
 
                     // set the redirect result and do not call next to short circuit
                     context.Result = pcr.IsRedirectPermanent()
-                        ? RedirectPermanent(pcr.RedirectUrl)
-                        : Redirect(pcr.RedirectUrl);
+                        ? RedirectPermanent(pcr.RedirectUrl!)
+                        : Redirect(pcr.RedirectUrl!);
                     break;
                 case UmbracoRouteResult.NotFound:
                     // set the redirect result and do not call next to short circuit
@@ -107,10 +107,10 @@ namespace Umbraco.Cms.Web.Common.Controllers
                     // If there it is means that we are proxying/executing this controller
                     // from another controller and we need to merge it's ViewData with this one
                     // since this one will be empty.
-                    ProxyViewDataFeature saveViewData = HttpContext.Features.Get<ProxyViewDataFeature>();
+                    ProxyViewDataFeature? saveViewData = HttpContext.Features.Get<ProxyViewDataFeature>();
                     if (saveViewData != null)
                     {
-                        foreach (KeyValuePair<string, object> kv in saveViewData.ViewData)
+                        foreach (KeyValuePair<string, object?> kv in saveViewData.ViewData)
                         {
                             ViewData[kv.Key] = kv.Value;
                         }
diff --git a/src/Umbraco.Web.Common/Controllers/UmbracoPageController.cs b/src/Umbraco.Web.Common/Controllers/UmbracoPageController.cs
index f9840df370..e10e3b5217 100644
--- a/src/Umbraco.Web.Common/Controllers/UmbracoPageController.cs
+++ b/src/Umbraco.Web.Common/Controllers/UmbracoPageController.cs
@@ -13,7 +13,7 @@ namespace Umbraco.Cms.Web.Common.Controllers
     /// </summary>
     public abstract class UmbracoPageController : UmbracoController
     {
-        private UmbracoRouteValues _umbracoRouteValues;
+        private UmbracoRouteValues? _umbracoRouteValues;
         private readonly ICompositeViewEngine _compositeViewEngine;
         private readonly ILogger<UmbracoPageController> _logger;
 
@@ -52,7 +52,7 @@ namespace Umbraco.Cms.Web.Common.Controllers
         /// <summary>
         /// Gets the current content item.
         /// </summary>
-        protected virtual IPublishedContent CurrentPage
+        protected virtual IPublishedContent? CurrentPage
         {
             get
             {
@@ -88,11 +88,11 @@ namespace Umbraco.Cms.Web.Common.Controllers
         /// Ensures that a physical view file exists on disk.
         /// </summary>
         /// <param name="template">The view name.</param>
-        protected bool EnsurePhsyicalViewExists(string template)
+        protected bool EnsurePhsyicalViewExists(string? template)
         {
             if (string.IsNullOrWhiteSpace(template))
             {
-                string docTypeAlias = UmbracoRouteValues.PublishedRequest.PublishedContent.ContentType.Alias;
+                string? docTypeAlias = UmbracoRouteValues.PublishedRequest.PublishedContent?.ContentType.Alias;
                 _logger.LogWarning("No physical template file was found for document type with alias {Alias}", docTypeAlias);
                 return false;
             }
diff --git a/src/Umbraco.Web.Common/DependencyInjection/ScopedServiceProvider.cs b/src/Umbraco.Web.Common/DependencyInjection/ScopedServiceProvider.cs
index de660184f1..5c9cf017af 100644
--- a/src/Umbraco.Web.Common/DependencyInjection/ScopedServiceProvider.cs
+++ b/src/Umbraco.Web.Common/DependencyInjection/ScopedServiceProvider.cs
@@ -12,6 +12,6 @@ namespace Umbraco.Cms.Web.Common.DependencyInjection
         public ScopedServiceProvider(IHttpContextAccessor accessor) => _accessor = accessor;
 
         /// <inheritdoc />
-        public IServiceProvider ServiceProvider => _accessor.HttpContext?.RequestServices;
+        public IServiceProvider? ServiceProvider => _accessor.HttpContext?.RequestServices;
     }
 }
diff --git a/src/Umbraco.Web.Common/DependencyInjection/UmbracoBuilder.ImageSharp.cs b/src/Umbraco.Web.Common/DependencyInjection/UmbracoBuilder.ImageSharp.cs
index 30331fd812..83144a7466 100644
--- a/src/Umbraco.Web.Common/DependencyInjection/UmbracoBuilder.ImageSharp.cs
+++ b/src/Umbraco.Web.Common/DependencyInjection/UmbracoBuilder.ImageSharp.cs
@@ -62,8 +62,11 @@ namespace Umbraco.Extensions
                         var headers = context.Response.GetTypedHeaders();
 
                         var cacheControl = headers.CacheControl;
-                        cacheControl.MustRevalidate = false;
-                        cacheControl.Extensions.Add(new NameValueHeaderValue("immutable"));
+                        if (cacheControl is not null)
+                        {
+                            cacheControl.MustRevalidate = false;
+                            cacheControl.Extensions.Add(new NameValueHeaderValue("immutable"));
+                        }
 
                         headers.CacheControl = cacheControl;
                     }
@@ -71,7 +74,7 @@ namespace Umbraco.Extensions
                     return Task.CompletedTask;
                 };
             })
-                .Configure<PhysicalFileSystemCacheOptions>(options => options.CacheFolder = builder.BuilderHostingEnvironment.MapPathContentRoot(imagingSettings.Cache.CacheFolder))
+                .Configure<PhysicalFileSystemCacheOptions>(options => options.CacheFolder = builder.BuilderHostingEnvironment?.MapPathContentRoot(imagingSettings.Cache.CacheFolder))
                 .AddProcessor<CropWebProcessor>();
 
             // Configure middleware to use the registered/shared ImageSharp configuration
diff --git a/src/Umbraco.Web.Common/DependencyInjection/UmbracoBuilderExtensions.cs b/src/Umbraco.Web.Common/DependencyInjection/UmbracoBuilderExtensions.cs
index 9f999e7167..5e2779e1dd 100644
--- a/src/Umbraco.Web.Common/DependencyInjection/UmbracoBuilderExtensions.cs
+++ b/src/Umbraco.Web.Common/DependencyInjection/UmbracoBuilderExtensions.cs
@@ -220,7 +220,7 @@ namespace Umbraco.Extensions
             return builder;
         }
 
-        public static IUmbracoBuilder AddMvcAndRazor(this IUmbracoBuilder builder, Action<IMvcBuilder> mvcBuilding = null)
+        public static IUmbracoBuilder AddMvcAndRazor(this IUmbracoBuilder builder, Action<IMvcBuilder>? mvcBuilding = null)
         {
             // TODO: We need to figure out if we can work around this because calling AddControllersWithViews modifies the global app and order is very important
             // this will directly affect developers who need to call that themselves.
@@ -344,7 +344,7 @@ namespace Umbraco.Extensions
             builder.Services.AddUnique<IBackOfficeSecurityAccessor, BackOfficeSecurityAccessor>();
 
             var umbracoApiControllerTypes = builder.TypeLoader.GetUmbracoApiControllers().ToList();
-            builder.WithCollectionBuilder<UmbracoApiControllerTypeCollectionBuilder>()
+            builder.WithCollectionBuilder<UmbracoApiControllerTypeCollectionBuilder>()?
                 .Add(umbracoApiControllerTypes);
 
             builder.Services.AddSingleton<UmbracoRequestLoggingMiddleware>();
diff --git a/src/Umbraco.Web.Common/Extensions/ApplicationBuilderExtensions.cs b/src/Umbraco.Web.Common/Extensions/ApplicationBuilderExtensions.cs
index 8f739ab542..fcd4dcb341 100644
--- a/src/Umbraco.Web.Common/Extensions/ApplicationBuilderExtensions.cs
+++ b/src/Umbraco.Web.Common/Extensions/ApplicationBuilderExtensions.cs
@@ -122,8 +122,12 @@ namespace Umbraco.Extensions
                     pluginFolder,
                     umbracoPluginSettings);
 
-                IWebHostEnvironment webHostEnvironment = app.ApplicationServices.GetService<IWebHostEnvironment>();
-                webHostEnvironment.WebRootFileProvider = webHostEnvironment.WebRootFileProvider.ConcatComposite(new PrependBasePathFileProvider(Constants.SystemDirectories.AppPlugins, pluginFileProvider));
+                IWebHostEnvironment? webHostEnvironment = app.ApplicationServices.GetService<IWebHostEnvironment>();
+
+                if (webHostEnvironment is not null)
+                {
+                    webHostEnvironment.WebRootFileProvider = webHostEnvironment.WebRootFileProvider.ConcatComposite(new PrependBasePathFileProvider(Constants.SystemDirectories.AppPlugins, pluginFileProvider));
+                }
             }
 
             return app;
diff --git a/src/Umbraco.Web.Common/Extensions/BlockListTemplateExtensions.cs b/src/Umbraco.Web.Common/Extensions/BlockListTemplateExtensions.cs
index 0fd5df73aa..c51a376145 100644
--- a/src/Umbraco.Web.Common/Extensions/BlockListTemplateExtensions.cs
+++ b/src/Umbraco.Web.Common/Extensions/BlockListTemplateExtensions.cs
@@ -11,7 +11,7 @@ namespace Umbraco.Extensions
         public const string DefaultFolder = "blocklist/";
         public const string DefaultTemplate = "default";
 
-        public static IHtmlContent GetBlockListHtml(this IHtmlHelper html, BlockListModel model, string template = DefaultTemplate)
+        public static IHtmlContent GetBlockListHtml(this IHtmlHelper html, BlockListModel? model, string template = DefaultTemplate)
         {
             if (model?.Count == 0) return new HtmlString(string.Empty);
 
diff --git a/src/Umbraco.Web.Common/Extensions/CacheHelperExtensions.cs b/src/Umbraco.Web.Common/Extensions/CacheHelperExtensions.cs
index 055e15ef73..e3c38c00ca 100644
--- a/src/Umbraco.Web.Common/Extensions/CacheHelperExtensions.cs
+++ b/src/Umbraco.Web.Common/Extensions/CacheHelperExtensions.cs
@@ -26,7 +26,7 @@ namespace Umbraco.Extensions
         /// <param name="cacheKey">used to cache the partial view, this key could change if it is cached by page or by member</param>
         /// <param name="viewData"></param>
         /// <returns></returns>
-        public static IHtmlContent CachedPartialView(
+        public static IHtmlContent? CachedPartialView(
             this AppCaches appCaches,
             IHostingEnvironment hostingEnvironment,
             IUmbracoContext umbracoContext,
@@ -35,7 +35,7 @@ namespace Umbraco.Extensions
             object model,
             TimeSpan cacheTimeout,
             string cacheKey,
-            ViewDataDictionary viewData = null
+            ViewDataDictionary? viewData = null
             )
         {
             //disable cached partials in debug mode: http://issues.umbraco.org/issue/U4-5940
diff --git a/src/Umbraco.Web.Common/Extensions/ControllerActionEndpointConventionBuilderExtensions.cs b/src/Umbraco.Web.Common/Extensions/ControllerActionEndpointConventionBuilderExtensions.cs
index 8da2e26b61..2436787296 100644
--- a/src/Umbraco.Web.Common/Extensions/ControllerActionEndpointConventionBuilderExtensions.cs
+++ b/src/Umbraco.Web.Common/Extensions/ControllerActionEndpointConventionBuilderExtensions.cs
@@ -24,7 +24,7 @@ namespace Umbraco.Extensions
                 if (convention.Metadata.OfType<ISuppressMatchingMetadata>().FirstOrDefault()?.SuppressMatching != true)
                 {
                     // Get the controller action descriptor
-                    ControllerActionDescriptor actionDescriptor = convention.Metadata.OfType<ControllerActionDescriptor>().FirstOrDefault();
+                    ControllerActionDescriptor? actionDescriptor = convention.Metadata.OfType<ControllerActionDescriptor>().FirstOrDefault();
                     if (actionDescriptor != null)
                     {
                         // This is more or less like the IApplicationModelProvider, it allows us to add filters, etc... to the ControllerActionDescriptor
diff --git a/src/Umbraco.Web.Common/Extensions/EndpointRouteBuilderExtensions.cs b/src/Umbraco.Web.Common/Extensions/EndpointRouteBuilderExtensions.cs
index c7b8190523..e984c3ae3f 100644
--- a/src/Umbraco.Web.Common/Extensions/EndpointRouteBuilderExtensions.cs
+++ b/src/Umbraco.Web.Common/Extensions/EndpointRouteBuilderExtensions.cs
@@ -19,7 +19,7 @@ namespace Umbraco.Extensions
             string prefixPathSegment,
             string defaultAction = "Index",
             bool includeControllerNameInRoute = true,
-            object constraints = null)
+            object? constraints = null)
         {
             var controllerName = ControllerExtensions.GetControllerName(controllerType);
 
@@ -75,7 +75,7 @@ namespace Umbraco.Extensions
             string prefixPathSegment,
             string defaultAction = "Index",
             bool includeControllerNameInRoute = true,
-            object constraints = null)
+            object? constraints = null)
             where T : ControllerBase
             => endpoints.MapUmbracoRoute(typeof(T), rootSegment, areaName, prefixPathSegment, defaultAction, includeControllerNameInRoute, constraints);
 
@@ -89,7 +89,7 @@ namespace Umbraco.Extensions
             string areaName,
             bool isBackOffice,
             string defaultAction = "Index",
-            object constraints = null)
+            object? constraints = null)
             where T : ControllerBase
             => endpoints.MapUmbracoApiRoute(typeof(T), rootSegment, areaName, isBackOffice, defaultAction, constraints);
 
@@ -103,7 +103,7 @@ namespace Umbraco.Extensions
             string areaName,
             bool isBackOffice,
             string defaultAction = "Index",
-            object constraints = null)
+            object? constraints = null)
         {
             string prefixPathSegment = isBackOffice
                 ? areaName.IsNullOrWhiteSpace()
@@ -130,7 +130,7 @@ namespace Umbraco.Extensions
             string areaName,
             string defaultAction = "Index",
             bool includeControllerNameInRoute = true,
-            object constraints = null)
+            object? constraints = null)
         {
             // If there is an area name it's a plugin controller, and we should use the area name instead of surface
             string prefixPathSegment = areaName.IsNullOrWhiteSpace() ? "Surface" : areaName;
diff --git a/src/Umbraco.Web.Common/Extensions/FormCollectionExtensions.cs b/src/Umbraco.Web.Common/Extensions/FormCollectionExtensions.cs
index 6a35f43758..a1d6ab4977 100644
--- a/src/Umbraco.Web.Common/Extensions/FormCollectionExtensions.cs
+++ b/src/Umbraco.Web.Common/Extensions/FormCollectionExtensions.cs
@@ -68,7 +68,7 @@ namespace Umbraco.Extensions
         /// <param name="items"></param>
         /// <param name="key"></param>
         /// <returns></returns>
-        public static T GetValue<T>(this FormCollection items, string key)
+        public static T? GetValue<T>(this FormCollection items, string key)
         {
             if (items.TryGetValue(key, out var val) == false || string.IsNullOrEmpty(val))
             {
@@ -97,7 +97,7 @@ namespace Umbraco.Extensions
 
             var converted = val.TryConvertTo<T>();
             return converted.Success
-                ? converted.Result
+                ? converted.Result!
                 : throw new InvalidOperationException($"The required query string parameter {key} cannot be converted to type {typeof(T)}");
         }
     }
diff --git a/src/Umbraco.Web.Common/Extensions/FriendlyImageCropperTemplateExtensions.cs b/src/Umbraco.Web.Common/Extensions/FriendlyImageCropperTemplateExtensions.cs
index c59e7b1126..dabefbc3ad 100644
--- a/src/Umbraco.Web.Common/Extensions/FriendlyImageCropperTemplateExtensions.cs
+++ b/src/Umbraco.Web.Common/Extensions/FriendlyImageCropperTemplateExtensions.cs
@@ -26,7 +26,7 @@ namespace Umbraco.Extensions
         /// <returns>
         /// The URL of the cropped image.
         /// </returns>
-        public static string GetCropUrl(
+        public static string? GetCropUrl(
             this IPublishedContent mediaItem,
             string cropAlias,
             UrlMode urlMode = UrlMode.Default) =>
@@ -41,7 +41,7 @@ namespace Umbraco.Extensions
         /// <returns>
         /// The URL of the cropped image.
         /// </returns>
-        public static string GetCropUrl(this MediaWithCrops mediaWithCrops, string cropAlias, UrlMode urlMode = UrlMode.Default)
+        public static string? GetCropUrl(this MediaWithCrops mediaWithCrops, string cropAlias, UrlMode urlMode = UrlMode.Default)
             => ImageCropperTemplateCoreExtensions.GetCropUrl(mediaWithCrops, cropAlias, ImageUrlGenerator, PublishedValueFallback, PublishedUrlProvider, urlMode);
 
         /// <summary>
@@ -54,7 +54,7 @@ namespace Umbraco.Extensions
         /// <returns>
         /// The image crop URL.
         /// </returns>
-        public static string GetCropUrl(
+        public static string? GetCropUrl(
             this IPublishedContent mediaItem,
             ImageCropperValue imageCropperValue,
             string cropAlias,
@@ -71,7 +71,7 @@ namespace Umbraco.Extensions
         /// <returns>
         /// The URL of the cropped image.
         /// </returns>
-        public static string GetCropUrl(
+        public static string? GetCropUrl(
             this IPublishedContent mediaItem,
             string propertyAlias,
             string cropAlias,
@@ -88,7 +88,7 @@ namespace Umbraco.Extensions
         /// <returns>
         /// The URL of the cropped image.
         /// </returns>
-        public static string GetCropUrl(this MediaWithCrops mediaWithCrops, string propertyAlias, string cropAlias, UrlMode urlMode = UrlMode.Default)
+        public static string? GetCropUrl(this MediaWithCrops mediaWithCrops, string propertyAlias, string cropAlias, UrlMode urlMode = UrlMode.Default)
             => ImageCropperTemplateCoreExtensions.GetCropUrl(mediaWithCrops, propertyAlias, cropAlias, ImageUrlGenerator, PublishedValueFallback, PublishedUrlProvider, urlMode);
 
         /// <summary>
@@ -113,19 +113,19 @@ namespace Umbraco.Extensions
         /// <returns>
         /// The URL of the cropped image.
         /// </returns>
-        public static string GetCropUrl(
+        public static string? GetCropUrl(
             this IPublishedContent mediaItem,
             int? width = null,
             int? height = null,
             string propertyAlias = Cms.Core.Constants.Conventions.Media.File,
-            string cropAlias = null,
+            string? cropAlias = null,
             int? quality = null,
             ImageCropMode? imageCropMode = null,
             ImageCropAnchor? imageCropAnchor = null,
             bool preferFocalPoint = false,
             bool useCropDimensions = false,
             bool cacheBuster = true,
-            string furtherOptions = null,
+            string? furtherOptions = null,
             UrlMode urlMode = UrlMode.Default)
             => mediaItem.GetCropUrl(
                 ImageUrlGenerator,
@@ -167,19 +167,19 @@ namespace Umbraco.Extensions
         /// <returns>
         /// The URL of the cropped image.
         /// </returns>
-        public static string GetCropUrl(
+        public static string? GetCropUrl(
             this MediaWithCrops mediaWithCrops,
             int? width = null,
             int? height = null,
             string propertyAlias = Cms.Core.Constants.Conventions.Media.File,
-            string cropAlias = null,
+            string? cropAlias = null,
             int? quality = null,
             ImageCropMode? imageCropMode = null,
             ImageCropAnchor? imageCropAnchor = null,
             bool preferFocalPoint = false,
             bool useCropDimensions = false,
             bool cacheBuster = true,
-            string furtherOptions = null,
+            string? furtherOptions = null,
             UrlMode urlMode = UrlMode.Default)
             => mediaWithCrops.GetCropUrl(
                 ImageUrlGenerator,
@@ -220,19 +220,19 @@ namespace Umbraco.Extensions
         /// <returns>
         /// The URL of the cropped image.
         /// </returns>
-        public static string GetCropUrl(
+        public static string? GetCropUrl(
             this string imageUrl,
             int? width = null,
             int? height = null,
-            string imageCropperValue = null,
-            string cropAlias = null,
+            string? imageCropperValue = null,
+            string? cropAlias = null,
             int? quality = null,
             ImageCropMode? imageCropMode = null,
             ImageCropAnchor? imageCropAnchor = null,
             bool preferFocalPoint = false,
             bool useCropDimensions = false,
-            string cacheBusterValue = null,
-            string furtherOptions = null)
+            string? cacheBusterValue = null,
+            string? furtherOptions = null)
             => imageUrl.GetCropUrl(
                 ImageUrlGenerator,
                 width,
@@ -269,19 +269,19 @@ namespace Umbraco.Extensions
         /// <returns>
         /// The URL of the cropped image.
         /// </returns>
-        public static string GetCropUrl(
+        public static string? GetCropUrl(
             this string imageUrl,
             ImageCropperValue cropDataSet,
             int? width = null,
             int? height = null,
-            string cropAlias = null,
+            string? cropAlias = null,
             int? quality = null,
             ImageCropMode? imageCropMode = null,
             ImageCropAnchor? imageCropAnchor = null,
             bool preferFocalPoint = false,
             bool useCropDimensions = false,
-            string cacheBusterValue = null,
-            string furtherOptions = null)
+            string? cacheBusterValue = null,
+            string? furtherOptions = null)
             => imageUrl.GetCropUrl(
                 ImageUrlGenerator,
                 cropDataSet,
@@ -301,6 +301,6 @@ namespace Umbraco.Extensions
         public static string GetLocalCropUrl(
             this MediaWithCrops mediaWithCrops,
             string alias,
-            string cacheBusterValue = null) => mediaWithCrops.LocalCrops.Src + mediaWithCrops.LocalCrops.GetCropUrl(alias, ImageUrlGenerator, cacheBusterValue: cacheBusterValue);
+            string? cacheBusterValue = null) => mediaWithCrops.LocalCrops.Src + mediaWithCrops.LocalCrops.GetCropUrl(alias, ImageUrlGenerator, cacheBusterValue: cacheBusterValue);
     }
 }
diff --git a/src/Umbraco.Web.Common/Extensions/FriendlyPublishedContentExtensions.cs b/src/Umbraco.Web.Common/Extensions/FriendlyPublishedContentExtensions.cs
index abbf934e04..ed53832cc5 100644
--- a/src/Umbraco.Web.Common/Extensions/FriendlyPublishedContentExtensions.cs
+++ b/src/Umbraco.Web.Common/Extensions/FriendlyPublishedContentExtensions.cs
@@ -50,7 +50,7 @@ namespace Umbraco.Extensions
         private static IPublishedValueFallback PublishedValueFallback { get; } =
             StaticServiceProvider.Instance.GetRequiredService<IPublishedValueFallback>();
 
-        private static IPublishedSnapshot PublishedSnapshot
+        private static IPublishedSnapshot? PublishedSnapshot
         {
             get
             {
@@ -75,7 +75,7 @@ namespace Umbraco.Extensions
         /// </summary>
         /// <param name="content">The internal published content.</param>
         /// <returns>The strongly typed published content model.</returns>
-        public static IPublishedContent CreateModel(
+        public static IPublishedContent? CreateModel(
             this IPublishedContent content)
             => content.CreateModel(PublishedModelFactory);
 
@@ -84,9 +84,9 @@ namespace Umbraco.Extensions
         /// </summary>
         /// <param name="content">The content item.</param>
         /// <param name="culture">The specific culture to get the name for. If null is used the current culture is used (Default is null).</param>
-        public static string Name(
+        public static string? Name(
             this IPublishedContent content,
-            string culture = null)
+            string? culture = null)
             => content.Name(VariationContextAccessor, culture);
 
         /// <summary>
@@ -94,9 +94,9 @@ namespace Umbraco.Extensions
         /// </summary>
         /// <param name="content">The content item.</param>
         /// <param name="culture">The specific culture to get the URL segment for. If null is used the current culture is used (Default is null).</param>
-        public static string UrlSegment(
+        public static string? UrlSegment(
             this IPublishedContent content,
-            string culture = null)
+            string? culture = null)
             => content.UrlSegment(VariationContextAccessor, culture);
 
         /// <summary>
@@ -106,7 +106,7 @@ namespace Umbraco.Extensions
         /// <param name="culture">The specific culture to get the name for. If null is used the current culture is used (Default is null).</param>
         public static DateTime CultureDate(
             this IPublishedContent content,
-            string culture = null)
+            string? culture = null)
             => content.CultureDate(VariationContextAccessor, culture);
 
         /// <summary>
@@ -159,8 +159,8 @@ namespace Umbraco.Extensions
         public static bool HasValue(
             this IPublishedContent content,
             string alias,
-            string culture = null,
-            string segment = null,
+            string? culture = null,
+            string? segment = null,
             Fallback fallback = default)
             =>
             content.HasValue(PublishedValueFallback, alias, culture, segment, fallback);
@@ -175,7 +175,7 @@ namespace Umbraco.Extensions
         /// <param name="fallback">Optional fallback strategy.</param>
         /// <param name="defaultValue">The default value.</param>
         /// <returns>The value of the content's property identified by the alias, if it exists, otherwise a default value.</returns>
-        public static object Value(this IPublishedContent content, string alias, string? culture = null, string? segment = null, Fallback fallback = default, object? defaultValue = default)
+        public static object? Value(this IPublishedContent content, string alias, string? culture = null, string? segment = null, Fallback fallback = default, object? defaultValue = default)
         => content.Value(PublishedValueFallback, alias, culture, segment, fallback, defaultValue);
 
         /// <summary>
@@ -189,7 +189,7 @@ namespace Umbraco.Extensions
         /// <param name="fallback">Optional fallback strategy.</param>
         /// <param name="defaultValue">The default value.</param>
         /// <returns>The value of the content's property identified by the alias, converted to the specified type.</returns>
-        public static T Value<T>(this IPublishedContent content, string alias, string? culture = null, string? segment = null, Fallback fallback = default, T defaultValue = default)
+        public static T? Value<T>(this IPublishedContent content, string alias, string? culture = null, string? segment = null, Fallback fallback = default, T? defaultValue = default)
             => content.Value<T>(PublishedValueFallback, alias, culture, segment, fallback, defaultValue);
 
         /// <summary>
@@ -218,7 +218,7 @@ namespace Umbraco.Extensions
         /// </remarks>
         public static IEnumerable<T> DescendantsOrSelf<T>(
             this IEnumerable<IPublishedContent> parentNodes,
-            string culture = null)
+            string? culture = null)
             where T : class, IPublishedContent
             => parentNodes.DescendantsOrSelf<T>(VariationContextAccessor, culture);
 
@@ -240,7 +240,7 @@ namespace Umbraco.Extensions
             where T : class, IPublishedContent
             => content.Descendants<T>(VariationContextAccessor, level, culture);
 
-        public static IEnumerable<IPublishedContent> DescendantsOrSelf(this IPublishedContent content,  string culture = null)
+        public static IEnumerable<IPublishedContent> DescendantsOrSelf(this IPublishedContent content,  string? culture = null)
             => content.DescendantsOrSelf(VariationContextAccessor, culture);
 
 
@@ -258,39 +258,39 @@ namespace Umbraco.Extensions
             where T : class, IPublishedContent
             => content.DescendantsOrSelf<T>(VariationContextAccessor, level, culture);
 
-        public static IPublishedContent Descendant(this IPublishedContent content, string? culture = null)
+        public static IPublishedContent? Descendant(this IPublishedContent content, string? culture = null)
             => content.Descendant(VariationContextAccessor, culture);
 
-        public static IPublishedContent Descendant(this IPublishedContent content, int level, string? culture = null)
+        public static IPublishedContent? Descendant(this IPublishedContent content, int level, string? culture = null)
             => content.Descendant(VariationContextAccessor, level, culture);
 
 
-        public static IPublishedContent DescendantOfType(this IPublishedContent content, string contentTypeAlias, string? culture = null)
+        public static IPublishedContent? DescendantOfType(this IPublishedContent content, string contentTypeAlias, string? culture = null)
             => content.DescendantOfType(VariationContextAccessor, contentTypeAlias, culture);
 
-        public static T Descendant<T>(this IPublishedContent content, string? culture = null)
+        public static T? Descendant<T>(this IPublishedContent content, string? culture = null)
             where T : class, IPublishedContent
             => content.Descendant<T>(VariationContextAccessor, culture);
 
 
-        public static T Descendant<T>(this IPublishedContent content, int level, string? culture = null)
+        public static T? Descendant<T>(this IPublishedContent content, int level, string? culture = null)
             where T : class, IPublishedContent
             => content.Descendant<T>(VariationContextAccessor, level, culture);
 
         public static IPublishedContent DescendantOrSelf(this IPublishedContent content, string? culture = null)
             => content.DescendantOrSelf(VariationContextAccessor, culture);
 
-        public static IPublishedContent DescendantOrSelf(this IPublishedContent content, int level, string? culture = null)
+        public static IPublishedContent? DescendantOrSelf(this IPublishedContent content, int level, string? culture = null)
             => content.DescendantOrSelf(VariationContextAccessor, level, culture);
 
-        public static IPublishedContent DescendantOrSelfOfType(this IPublishedContent content, string contentTypeAlias, string? culture = null)
+        public static IPublishedContent? DescendantOrSelfOfType(this IPublishedContent content, string contentTypeAlias, string? culture = null)
             => content.DescendantOrSelfOfType(VariationContextAccessor, contentTypeAlias, culture);
 
-        public static T DescendantOrSelf<T>(this IPublishedContent content, string? culture = null)
+        public static T? DescendantOrSelf<T>(this IPublishedContent content, string? culture = null)
             where T : class, IPublishedContent
             => content.DescendantOrSelf<T>(VariationContextAccessor, culture);
 
-        public static T DescendantOrSelf<T>(this IPublishedContent content, int level, string? culture = null)
+        public static T? DescendantOrSelf<T>(this IPublishedContent content, int level, string? culture = null)
             where T : class, IPublishedContent
             => content.DescendantOrSelf<T>(VariationContextAccessor, level, culture);
 
@@ -317,7 +317,7 @@ namespace Umbraco.Extensions
         /// However, if an empty string is specified only invariant children are returned.
         /// </para>
         /// </remarks>
-        public static IEnumerable<IPublishedContent> Children(this IPublishedContent content, string? culture = null)
+        public static IEnumerable<IPublishedContent>? Children(this IPublishedContent content, string? culture = null)
             => content.Children(VariationContextAccessor, culture);
 
         /// <summary>
@@ -330,7 +330,7 @@ namespace Umbraco.Extensions
         /// <remarks>
         /// <para>Children are sorted by their sortOrder.</para>
         /// </remarks>
-        public static IEnumerable<IPublishedContent> Children(this IPublishedContent content, Func<IPublishedContent, bool> predicate, string? culture = null)
+        public static IEnumerable<IPublishedContent>? Children(this IPublishedContent content, Func<IPublishedContent, bool> predicate, string? culture = null)
             => content.Children(VariationContextAccessor, predicate, culture);
 
         /// <summary>
@@ -340,7 +340,7 @@ namespace Umbraco.Extensions
         /// <param name="culture">The specific culture to filter for. If null is used the current culture is used. (Default is null)</param>
         /// <param name="contentTypeAlias">The content type alias.</param>
         /// <returns>The children of the content, of any of the specified types.</returns>
-        public static IEnumerable<IPublishedContent> ChildrenOfType(this IPublishedContent content, string contentTypeAlias, string? culture = null)
+        public static IEnumerable<IPublishedContent>? ChildrenOfType(this IPublishedContent content, string contentTypeAlias, string? culture = null)
             => content.ChildrenOfType(VariationContextAccessor, contentTypeAlias, culture);
 
         /// <summary>
@@ -353,31 +353,31 @@ namespace Umbraco.Extensions
         /// <remarks>
         /// <para>Children are sorted by their sortOrder.</para>
         /// </remarks>
-        public static IEnumerable<T> Children<T>(this IPublishedContent content, string? culture = null)
+        public static IEnumerable<T>? Children<T>(this IPublishedContent content, string? culture = null)
             where T : class, IPublishedContent
             => content.Children<T>(VariationContextAccessor, culture);
 
-        public static IPublishedContent FirstChild(this IPublishedContent content, string? culture = null)
+        public static IPublishedContent? FirstChild(this IPublishedContent content, string? culture = null)
             => content.FirstChild(VariationContextAccessor, culture);
 
         /// <summary>
         /// Gets the first child of the content, of a given content type.
         /// </summary>
-        public static IPublishedContent FirstChildOfType(this IPublishedContent content, string contentTypeAlias, string? culture = null)
+        public static IPublishedContent? FirstChildOfType(this IPublishedContent content, string contentTypeAlias, string? culture = null)
             => content.FirstChildOfType(VariationContextAccessor, contentTypeAlias, culture);
 
-        public static IPublishedContent FirstChild(this IPublishedContent content, Func<IPublishedContent, bool> predicate, string? culture = null)
+        public static IPublishedContent? FirstChild(this IPublishedContent content, Func<IPublishedContent, bool> predicate, string? culture = null)
             => content.FirstChild(VariationContextAccessor, predicate, culture);
 
-        public static IPublishedContent FirstChild(this IPublishedContent content, Guid uniqueId, string? culture = null)
+        public static IPublishedContent? FirstChild(this IPublishedContent content, Guid uniqueId, string? culture = null)
             => content.FirstChild(VariationContextAccessor, uniqueId, culture);
 
 
-        public static T FirstChild<T>(this IPublishedContent content, string? culture = null)
+        public static T? FirstChild<T>(this IPublishedContent content, string? culture = null)
             where T : class, IPublishedContent
             => content.FirstChild<T>(VariationContextAccessor, culture);
 
-        public static T FirstChild<T>(this IPublishedContent content, Func<T, bool> predicate, string? culture = null)
+        public static T? FirstChild<T>(this IPublishedContent content, Func<T, bool> predicate, string? culture = null)
             where T : class, IPublishedContent
             => content.FirstChild<T>(VariationContextAccessor, predicate, culture);
 
@@ -390,7 +390,7 @@ namespace Umbraco.Extensions
         /// <remarks>
         ///   <para>Note that in V7 this method also return the content node self.</para>
         /// </remarks>
-        public static IEnumerable<IPublishedContent> Siblings(this IPublishedContent content, string? culture = null)
+        public static IEnumerable<IPublishedContent>? Siblings(this IPublishedContent content, string? culture = null)
             => content.Siblings(PublishedSnapshot, VariationContextAccessor, culture);
 
         /// <summary>
@@ -403,7 +403,7 @@ namespace Umbraco.Extensions
         /// <remarks>
         ///   <para>Note that in V7 this method also return the content node self.</para>
         /// </remarks>
-        public static IEnumerable<IPublishedContent> SiblingsOfType(this IPublishedContent content, string contentTypeAlias, string? culture = null)
+        public static IEnumerable<IPublishedContent>? SiblingsOfType(this IPublishedContent content, string contentTypeAlias, string? culture = null)
             => content.SiblingsOfType(PublishedSnapshot, VariationContextAccessor, contentTypeAlias, culture);
 
         /// <summary>
@@ -416,7 +416,7 @@ namespace Umbraco.Extensions
         /// <remarks>
         ///   <para>Note that in V7 this method also return the content node self.</para>
         /// </remarks>
-        public static IEnumerable<T> Siblings<T>(this IPublishedContent content, string? culture = null)
+        public static IEnumerable<T>? Siblings<T>(this IPublishedContent content, string? culture = null)
             where T : class, IPublishedContent
             => content.Siblings<T>(PublishedSnapshot, VariationContextAccessor, culture);
 
@@ -426,7 +426,7 @@ namespace Umbraco.Extensions
         /// <param name="content">The content.</param>
         /// <param name="culture">The specific culture to filter for. If null is used the current culture is used. (Default is null)</param>
         /// <returns>The siblings of the content including the node itself.</returns>
-        public static IEnumerable<IPublishedContent> SiblingsAndSelf(this IPublishedContent content, string? culture = null)
+        public static IEnumerable<IPublishedContent>? SiblingsAndSelf(this IPublishedContent content, string? culture = null)
             => content.SiblingsAndSelf(PublishedSnapshot, VariationContextAccessor, culture);
 
         /// <summary>
@@ -436,7 +436,7 @@ namespace Umbraco.Extensions
         /// <param name="culture">The specific culture to filter for. If null is used the current culture is used. (Default is null)</param>
         /// <param name="contentTypeAlias">The content type alias.</param>
         /// <returns>The siblings of the content including the node itself, of the given content type.</returns>
-        public static IEnumerable<IPublishedContent> SiblingsAndSelfOfType(this IPublishedContent content, string contentTypeAlias, string? culture = null)
+        public static IEnumerable<IPublishedContent>? SiblingsAndSelfOfType(this IPublishedContent content, string contentTypeAlias, string? culture = null)
             => content.SiblingsAndSelfOfType(PublishedSnapshot, VariationContextAccessor, contentTypeAlias, culture);
 
         /// <summary>
@@ -446,7 +446,7 @@ namespace Umbraco.Extensions
         /// <param name="content">The content.</param>
         /// <param name="culture">The specific culture to filter for. If null is used the current culture is used. (Default is null)</param>
         /// <returns>The siblings of the content including the node itself, of the given content type.</returns>
-        public static IEnumerable<T> SiblingsAndSelf<T>(this IPublishedContent content, string? culture = null)
+        public static IEnumerable<T>? SiblingsAndSelf<T>(this IPublishedContent content, string? culture = null)
             where T : class, IPublishedContent
             => content.SiblingsAndSelf<T>(PublishedSnapshot, VariationContextAccessor, culture);
 
@@ -496,7 +496,7 @@ namespace Umbraco.Extensions
         /// </remarks>
         public static string MediaUrl(
             this IPublishedContent content,
-            string culture = null,
+            string? culture = null,
             UrlMode mode = UrlMode.Default,
             string propertyAlias = Constants.Conventions.Media.File)
             => content.MediaUrl(PublishedUrlProvider, culture, mode, propertyAlias);
@@ -505,14 +505,14 @@ namespace Umbraco.Extensions
         /// Gets the name of the content item creator.
         /// </summary>
         /// <param name="content">The content item.</param>
-        public static string CreatorName(this IPublishedContent content) =>
+        public static string? CreatorName(this IPublishedContent content) =>
             content.CreatorName(UserService);
 
         /// <summary>
         /// Gets the name of the content item writer.
         /// </summary>
         /// <param name="content">The content item.</param>
-        public static string WriterName(this IPublishedContent content) =>
+        public static string? WriterName(this IPublishedContent content) =>
             content.WriterName(UserService);
 
         /// <summary>
@@ -526,23 +526,23 @@ namespace Umbraco.Extensions
         /// one document per culture), and domains, withing the context of a current Uri, assign
         /// a culture to that document.</para>
         /// </remarks>
-        public static string GetCultureFromDomains(
+        public static string? GetCultureFromDomains(
             this IPublishedContent content,
-            Uri current = null)
+            Uri? current = null)
             => content.GetCultureFromDomains(UmbracoContextAccessor, SiteDomainHelper, current);
 
 
         public static IEnumerable<PublishedSearchResult> SearchDescendants(
             this IPublishedContent content,
             string term,
-            string indexName = null)
+            string? indexName = null)
             => content.SearchDescendants(ExamineManager, UmbracoContextAccessor, term, indexName);
 
 
         public static IEnumerable<PublishedSearchResult> SearchChildren(
             this IPublishedContent content,
             string term,
-            string indexName = null)
+            string? indexName = null)
             => content.SearchChildren(ExamineManager, UmbracoContextAccessor, term, indexName);
 
 
diff --git a/src/Umbraco.Web.Common/Extensions/FriendlyPublishedElementExtensions.cs b/src/Umbraco.Web.Common/Extensions/FriendlyPublishedElementExtensions.cs
index 4d4f5e1992..fe10a33837 100644
--- a/src/Umbraco.Web.Common/Extensions/FriendlyPublishedElementExtensions.cs
+++ b/src/Umbraco.Web.Common/Extensions/FriendlyPublishedElementExtensions.cs
@@ -27,11 +27,11 @@ namespace Umbraco.Extensions
         /// <para>If eg a numeric property wants to default to 0 when value source is empty, this has to be done in the converter.</para>
         /// <para>The alias is case-insensitive.</para>
         /// </remarks>
-        public static object Value(
+        public static object? Value(
             this IPublishedElement content,
             string alias,
-            string culture = null,
-            string segment = null,
+            string? culture = null,
+            string? segment = null,
             Fallback fallback = default,
             object? defaultValue = default)
             => content.Value(PublishedValueFallback, alias, culture, segment, fallback, defaultValue);
@@ -53,13 +53,13 @@ namespace Umbraco.Extensions
         /// <para>If eg a numeric property wants to default to 0 when value source is empty, this has to be done in the converter.</para>
         /// <para>The alias is case-insensitive.</para>
         /// </remarks>
-        public static T Value<T>(
+        public static T? Value<T>(
             this IPublishedElement content,
             string alias,
-            string culture = null,
-            string segment = null,
+            string? culture = null,
+            string? segment = null,
             Fallback fallback = default,
-            T defaultValue = default)
+            T? defaultValue = default)
             => content.Value<T>(PublishedValueFallback, alias, culture, segment, fallback, defaultValue);
 
         /// <summary>
@@ -75,7 +75,7 @@ namespace Umbraco.Extensions
         /// <summary>
         /// Gets the value of a property.
         /// </summary>
-        public static TValue ValueFor<TModel, TValue>(this TModel model, Expression<Func<TModel, TValue>> property, string? culture = null, string? segment = null, Fallback fallback = default, TValue defaultValue = default)
+        public static TValue? ValueFor<TModel, TValue>(this TModel model, Expression<Func<TModel, TValue>> property, string? culture = null, string? segment = null, Fallback fallback = default, TValue? defaultValue = default)
             where TModel : IPublishedElement =>
             model.ValueFor(PublishedValueFallback, property, culture, segment, fallback);
     }
diff --git a/src/Umbraco.Web.Common/Extensions/HttpContextExtensions.cs b/src/Umbraco.Web.Common/Extensions/HttpContextExtensions.cs
index d6beb90c01..2a2f82e576 100644
--- a/src/Umbraco.Web.Common/Extensions/HttpContextExtensions.cs
+++ b/src/Umbraco.Web.Common/Extensions/HttpContextExtensions.cs
@@ -14,7 +14,7 @@ namespace Umbraco.Extensions
         /// <summary>
         /// Try to get the basic auth username and password from the http context.
         /// </summary>
-        public static bool TryGetBasicAuthCredentials(this HttpContext httpContext, out string username, out string password)
+        public static bool TryGetBasicAuthCredentials(this HttpContext httpContext, out string? username, out string? password)
         {
             username = null;
             password = null;
@@ -70,9 +70,12 @@ namespace Umbraco.Extensions
             return value ?? request.Query[key];
         }
 
-        public static void SetPrincipalForRequest(this HttpContext context, ClaimsPrincipal principal)
+        public static void SetPrincipalForRequest(this HttpContext context, ClaimsPrincipal? principal)
         {
-            context.User = principal;
+            if (principal is not null)
+            {
+                context.User = principal;
+            }
         }
 
 
@@ -94,7 +97,7 @@ namespace Umbraco.Extensions
         /// <returns>
         /// Returns the current back office identity if an admin is authenticated otherwise null
         /// </returns>
-        public static ClaimsIdentity GetCurrentIdentity(this HttpContext http)
+        public static ClaimsIdentity? GetCurrentIdentity(this HttpContext http)
         {
             if (http == null) throw new ArgumentNullException(nameof(http));
             if (http.User == null) return null; //there's no user at all so no identity
diff --git a/src/Umbraco.Web.Common/Extensions/HttpRequestExtensions.cs b/src/Umbraco.Web.Common/Extensions/HttpRequestExtensions.cs
index 7d9ce136ef..b511ccf8f1 100644
--- a/src/Umbraco.Web.Common/Extensions/HttpRequestExtensions.cs
+++ b/src/Umbraco.Web.Common/Extensions/HttpRequestExtensions.cs
@@ -29,8 +29,8 @@ namespace Umbraco.Extensions
         public static bool IsBackOfficeRequest(this HttpRequest request)
         {
             PathString absPath = request.Path;
-            UmbracoRequestPaths umbReqPaths = request.HttpContext.RequestServices.GetService<UmbracoRequestPaths>();
-            return umbReqPaths.IsBackOfficeRequest(absPath);
+            UmbracoRequestPaths? umbReqPaths = request.HttpContext.RequestServices.GetService<UmbracoRequestPaths>();
+            return umbReqPaths?.IsBackOfficeRequest(absPath) ?? false;
         }
 
         /// <summary>
@@ -39,11 +39,11 @@ namespace Umbraco.Extensions
         public static bool IsClientSideRequest(this HttpRequest request)
         {
             PathString absPath = request.Path;
-            UmbracoRequestPaths umbReqPaths = request.HttpContext.RequestServices.GetService<UmbracoRequestPaths>();
-            return umbReqPaths.IsClientSideRequest(absPath);
+            UmbracoRequestPaths? umbReqPaths = request.HttpContext.RequestServices.GetService<UmbracoRequestPaths>();
+            return umbReqPaths?.IsClientSideRequest(absPath) ?? false;
         }
 
-        public static string ClientCulture(this HttpRequest request)
+        public static string? ClientCulture(this HttpRequest request)
             => request.Headers.TryGetValue("X-UMB-CULTURE", out var values) ? values[0] : null;
 
         /// <summary>
@@ -56,10 +56,10 @@ namespace Umbraco.Extensions
         public static bool IsLocal(this HttpRequest request)
         {
             var connection = request.HttpContext.Connection;
-            if (connection.RemoteIpAddress.IsSet())
+            if (connection.RemoteIpAddress?.IsSet() ?? false)
             {
                 // We have a remote address set up
-                return connection.LocalIpAddress.IsSet()
+                return connection.LocalIpAddress?.IsSet() ?? false
                     // Is local is same as remote, then we are local
                     ? connection.RemoteIpAddress.Equals(connection.LocalIpAddress)
                     // else we are remote if the remote IP address is not a loopback address
@@ -75,7 +75,7 @@ namespace Umbraco.Extensions
             return address != null && address.ToString() != NullIpAddress;
         }
 
-        public static string GetRawBodyString(this HttpRequest request, Encoding encoding = null)
+        public static string GetRawBodyString(this HttpRequest request, Encoding? encoding = null)
         {
             if (request.Body.CanSeek)
             {
@@ -94,7 +94,7 @@ namespace Umbraco.Extensions
             }
         }
 
-        public static async Task<string> GetRawBodyStringAsync(this HttpRequest request, Encoding encoding = null)
+        public static async Task<string> GetRawBodyStringAsync(this HttpRequest request, Encoding? encoding = null)
         {
             if (!request.Body.CanSeek)
             {
@@ -143,7 +143,7 @@ namespace Umbraco.Extensions
         /// </summary>
         /// <param name="request">The current request</param>
         /// <returns>The extracted `ufprt` token.</returns>
-        public static string GetUfprt(this HttpRequest request)
+        public static string? GetUfprt(this HttpRequest request)
         {
             if (request.HasFormContentType && request.Form.TryGetValue("ufprt", out StringValues formVal) && formVal != StringValues.Empty)
             {
diff --git a/src/Umbraco.Web.Common/Extensions/IdentityBuilderExtensions.cs b/src/Umbraco.Web.Common/Extensions/IdentityBuilderExtensions.cs
index 9b80f3e82a..5ec7adc1f3 100644
--- a/src/Umbraco.Web.Common/Extensions/IdentityBuilderExtensions.cs
+++ b/src/Umbraco.Web.Common/Extensions/IdentityBuilderExtensions.cs
@@ -20,6 +20,7 @@ namespace Umbraco.Extensions
         /// <returns>The current <see cref="IdentityBuilder"/> instance.</returns>
         public static IdentityBuilder AddMemberManager<TInterface, TUserManager>(this IdentityBuilder identityBuilder)
             where TUserManager : UserManager<MemberIdentityUser>, TInterface
+            where TInterface : notnull
         {
             identityBuilder.AddUserManager<TUserManager>();
             // use a UniqueServiceDescriptor so we can check if it's already been added
@@ -31,6 +32,7 @@ namespace Umbraco.Extensions
 
         public static IdentityBuilder AddRoleManager<TInterface, TRoleManager>(this IdentityBuilder identityBuilder)
             where TRoleManager : RoleManager<UmbracoIdentityRole>, TInterface
+            where TInterface : notnull
         {
             identityBuilder.AddRoleManager<TRoleManager>();
             identityBuilder.Services.AddScoped(typeof(TInterface), typeof(TRoleManager));
diff --git a/src/Umbraco.Web.Common/Extensions/ImageCropperTemplateCoreExtensions.cs b/src/Umbraco.Web.Common/Extensions/ImageCropperTemplateCoreExtensions.cs
index f335a81ae7..57779d2082 100644
--- a/src/Umbraco.Web.Common/Extensions/ImageCropperTemplateCoreExtensions.cs
+++ b/src/Umbraco.Web.Common/Extensions/ImageCropperTemplateCoreExtensions.cs
@@ -24,7 +24,7 @@ namespace Umbraco.Extensions
         /// <returns>
         /// The URL of the cropped image.
         /// </returns>
-        public static string GetCropUrl(
+        public static string? GetCropUrl(
             this IPublishedContent mediaItem,
             string cropAlias,
             IImageUrlGenerator imageUrlGenerator,
@@ -44,7 +44,7 @@ namespace Umbraco.Extensions
         /// <returns>
         /// The URL of the cropped image.
         /// </returns>
-        public static string GetCropUrl(
+        public static string? GetCropUrl(
             this MediaWithCrops mediaWithCrops,
             string cropAlias,
             IImageUrlGenerator imageUrlGenerator,
@@ -65,7 +65,7 @@ namespace Umbraco.Extensions
         /// <returns>
         /// The image crop URL.
         /// </returns>
-        public static string GetCropUrl(
+        public static string? GetCropUrl(
             this IPublishedContent mediaItem,
             ImageCropperValue imageCropperValue,
             string cropAlias,
@@ -87,7 +87,7 @@ namespace Umbraco.Extensions
         /// <returns>
         /// The URL of the cropped image.
         /// </returns>
-        public static string GetCropUrl(
+        public static string? GetCropUrl(
             this IPublishedContent mediaItem,
             string propertyAlias,
             string cropAlias,
@@ -109,7 +109,7 @@ namespace Umbraco.Extensions
         /// <returns>
         /// The URL of the cropped image.
         /// </returns>
-        public static string GetCropUrl(this MediaWithCrops mediaWithCrops,
+        public static string? GetCropUrl(this MediaWithCrops mediaWithCrops,
             IPublishedValueFallback publishedValueFallback,
             IPublishedUrlProvider publishedUrlProvider,
             string propertyAlias,
@@ -142,7 +142,7 @@ namespace Umbraco.Extensions
         /// <returns>
         /// The URL of the cropped image.
         /// </returns>
-        public static string GetCropUrl(
+        public static string? GetCropUrl(
              this IPublishedContent mediaItem,
              IImageUrlGenerator imageUrlGenerator,
              IPublishedValueFallback publishedValueFallback,
@@ -150,14 +150,14 @@ namespace Umbraco.Extensions
              int? width = null,
              int? height = null,
              string propertyAlias = Cms.Core.Constants.Conventions.Media.File,
-             string cropAlias = null,
+             string? cropAlias = null,
              int? quality = null,
              ImageCropMode? imageCropMode = null,
              ImageCropAnchor? imageCropAnchor = null,
              bool preferFocalPoint = false,
              bool useCropDimensions = false,
              bool cacheBuster = true,
-             string furtherOptions = null,
+             string? furtherOptions = null,
              UrlMode urlMode = UrlMode.Default) => mediaItem.GetCropUrl(imageUrlGenerator, publishedValueFallback, publishedUrlProvider, null, false, width, height, propertyAlias, cropAlias, quality, imageCropMode, imageCropAnchor, preferFocalPoint, useCropDimensions, cacheBuster, furtherOptions, urlMode);
 
         /// <summary>
@@ -185,7 +185,7 @@ namespace Umbraco.Extensions
         /// <returns>
         /// The URL of the cropped image.
         /// </returns>
-        public static string GetCropUrl(
+        public static string? GetCropUrl(
              this MediaWithCrops mediaWithCrops,
              IImageUrlGenerator imageUrlGenerator,
              IPublishedValueFallback publishedValueFallback,
@@ -193,14 +193,14 @@ namespace Umbraco.Extensions
              int? width = null,
              int? height = null,
              string propertyAlias = Constants.Conventions.Media.File,
-             string cropAlias = null,
+             string? cropAlias = null,
              int? quality = null,
              ImageCropMode? imageCropMode = null,
              ImageCropAnchor? imageCropAnchor = null,
              bool preferFocalPoint = false,
              bool useCropDimensions = false,
              bool cacheBuster = true,
-             string furtherOptions = null,
+             string? furtherOptions = null,
              UrlMode urlMode = UrlMode.Default)
         {
             if (mediaWithCrops == null)
@@ -211,24 +211,24 @@ namespace Umbraco.Extensions
             return mediaWithCrops.Content.GetCropUrl(imageUrlGenerator, publishedValueFallback, publishedUrlProvider, mediaWithCrops.LocalCrops, false, width, height, propertyAlias, cropAlias, quality, imageCropMode, imageCropAnchor, preferFocalPoint, useCropDimensions, cacheBuster, furtherOptions, urlMode);
         }
 
-        private static string GetCropUrl(
+        private static string? GetCropUrl(
              this IPublishedContent mediaItem,
              IImageUrlGenerator imageUrlGenerator,
              IPublishedValueFallback publishedValueFallback,
              IPublishedUrlProvider publishedUrlProvider,
-             ImageCropperValue localCrops,
+             ImageCropperValue? localCrops,
              bool localCropsOnly,
              int? width = null,
              int? height = null,
              string propertyAlias = Constants.Conventions.Media.File,
-             string cropAlias = null,
+             string? cropAlias = null,
              int? quality = null,
              ImageCropMode? imageCropMode = null,
              ImageCropAnchor? imageCropAnchor = null,
              bool preferFocalPoint = false,
              bool useCropDimensions = false,
              bool cacheBuster = true,
-             string furtherOptions = null,
+             string? furtherOptions = null,
              UrlMode urlMode = UrlMode.Default)
         {
             if (mediaItem == null)
@@ -302,27 +302,27 @@ namespace Umbraco.Extensions
         /// <returns>
         /// The URL of the cropped image.
         /// </returns>
-        public static string GetCropUrl(
+        public static string? GetCropUrl(
             this string imageUrl,
             IImageUrlGenerator imageUrlGenerator,
             int? width = null,
             int? height = null,
-            string imageCropperValue = null,
-            string cropAlias = null,
+            string? imageCropperValue = null,
+            string? cropAlias = null,
             int? quality = null,
             ImageCropMode? imageCropMode = null,
             ImageCropAnchor? imageCropAnchor = null,
             bool preferFocalPoint = false,
             bool useCropDimensions = false,
-            string cacheBusterValue = null,
-            string furtherOptions = null)
+            string? cacheBusterValue = null,
+            string? furtherOptions = null)
         {
             if (string.IsNullOrWhiteSpace(imageUrl))
             {
                 return null;
             }
 
-            ImageCropperValue cropDataSet = null;
+            ImageCropperValue? cropDataSet = null;
             if (string.IsNullOrEmpty(imageCropperValue) == false && imageCropperValue.DetectIsJson() && (imageCropMode == ImageCropMode.Crop || imageCropMode == null))
             {
                 cropDataSet = imageCropperValue.DeserializeImageCropperValue();
@@ -355,20 +355,20 @@ namespace Umbraco.Extensions
         /// <returns>
         /// The URL of the cropped image.
         /// </returns>
-        public static string GetCropUrl(
+        public static string? GetCropUrl(
             this string imageUrl,
             IImageUrlGenerator imageUrlGenerator,
-            ImageCropperValue cropDataSet,
+            ImageCropperValue? cropDataSet,
             int? width = null,
             int? height = null,
-            string cropAlias = null,
+            string? cropAlias = null,
             int? quality = null,
             ImageCropMode? imageCropMode = null,
             ImageCropAnchor? imageCropAnchor = null,
             bool preferFocalPoint = false,
             bool useCropDimensions = false,
-            string cacheBusterValue = null,
-            string furtherOptions = null)
+            string? cacheBusterValue = null,
+            string? furtherOptions = null)
         {
             if (string.IsNullOrWhiteSpace(imageUrl))
             {
@@ -378,7 +378,7 @@ namespace Umbraco.Extensions
             ImageUrlGenerationOptions options;
             if (cropDataSet != null && (imageCropMode == ImageCropMode.Crop || imageCropMode == null))
             {
-                ImageCropperValue.ImageCropperCrop crop = cropDataSet.GetCrop(cropAlias);
+                ImageCropperValue.ImageCropperCrop? crop = cropDataSet.GetCrop(cropAlias);
 
                 // If a crop was specified, but not found, return null
                 if (crop == null && !string.IsNullOrWhiteSpace(cropAlias))
diff --git a/src/Umbraco.Web.Common/Extensions/ImageCropperTemplateExtensions.cs b/src/Umbraco.Web.Common/Extensions/ImageCropperTemplateExtensions.cs
index 82bb8d2c01..e7b08c51f1 100644
--- a/src/Umbraco.Web.Common/Extensions/ImageCropperTemplateExtensions.cs
+++ b/src/Umbraco.Web.Common/Extensions/ImageCropperTemplateExtensions.cs
@@ -21,7 +21,7 @@ namespace Umbraco.Extensions
 
         internal static ImageCropperValue DeserializeImageCropperValue(this string json)
         {
-            ImageCropperValue imageCrops = null;
+            ImageCropperValue? imageCrops = null;
 
             if (json.DetectIsJson())
             {
diff --git a/src/Umbraco.Web.Common/Extensions/LinkGeneratorExtensions.cs b/src/Umbraco.Web.Common/Extensions/LinkGeneratorExtensions.cs
index c30eefd918..71f1d5410a 100644
--- a/src/Umbraco.Web.Common/Extensions/LinkGeneratorExtensions.cs
+++ b/src/Umbraco.Web.Common/Extensions/LinkGeneratorExtensions.cs
@@ -18,10 +18,10 @@ namespace Umbraco.Extensions
         /// <summary>
         /// Return the back office url if the back office is installed
         /// </summary>
-        public static string GetBackOfficeUrl(this LinkGenerator linkGenerator, IHostingEnvironment hostingEnvironment)
+        public static string? GetBackOfficeUrl(this LinkGenerator linkGenerator, IHostingEnvironment hostingEnvironment)
         {
 
-            Type backOfficeControllerType;
+            Type? backOfficeControllerType;
             try
             {
                 backOfficeControllerType = Assembly.Load("Umbraco.Web.BackOffice")?.GetType("Umbraco.Web.BackOffice.Controllers.BackOfficeController");
@@ -42,19 +42,19 @@ namespace Umbraco.Extensions
         /// Return the Url for a Web Api service
         /// </summary>
         /// <typeparam name="T">The <see cref="UmbracoApiControllerBase"/></typeparam>
-        public static string GetUmbracoApiService<T>(this LinkGenerator linkGenerator, string actionName, object id = null)
+        public static string? GetUmbracoApiService<T>(this LinkGenerator linkGenerator, string actionName, object? id = null)
             where T : UmbracoApiControllerBase => linkGenerator.GetUmbracoControllerUrl(
                 actionName,
                 typeof(T),
-                new Dictionary<string, object>()
+                new Dictionary<string, object?>()
                 {
                     ["id"] = id
                 });
 
-        public static string GetUmbracoApiService<T>(this LinkGenerator linkGenerator, string actionName, IDictionary<string, object> values)
+        public static string? GetUmbracoApiService<T>(this LinkGenerator linkGenerator, string actionName, IDictionary<string, object?>? values)
             where T : UmbracoApiControllerBase => linkGenerator.GetUmbracoControllerUrl(actionName, typeof(T), values);
 
-        public static string GetUmbracoApiServiceBaseUrl<T>(this LinkGenerator linkGenerator, Expression<Func<T, object>> methodSelector)
+        public static string? GetUmbracoApiServiceBaseUrl<T>(this LinkGenerator linkGenerator, Expression<Func<T, object>> methodSelector)
             where T : UmbracoApiControllerBase
         {
             var method = ExpressionHelper.GetMethodInfo(methodSelector);
@@ -62,13 +62,13 @@ namespace Umbraco.Extensions
             {
                 throw new MissingMethodException("Could not find the method " + methodSelector + " on type " + typeof(T) + " or the result ");
             }
-            return linkGenerator.GetUmbracoApiService<T>(method.Name).TrimEnd(method.Name);
+            return linkGenerator.GetUmbracoApiService<T>(method.Name)?.TrimEnd(method.Name);
         }
 
         /// <summary>
         /// Return the Url for an Umbraco controller
         /// </summary>
-        public static string GetUmbracoControllerUrl(this LinkGenerator linkGenerator, string actionName, string controllerName, string area, IDictionary<string, object> dict = null)
+        public static string? GetUmbracoControllerUrl(this LinkGenerator linkGenerator, string actionName, string controllerName, string? area, IDictionary<string, object?>? dict = null)
         {
             if (actionName == null)
             {
@@ -92,16 +92,16 @@ namespace Umbraco.Extensions
 
             if (dict is null)
             {
-                dict = new Dictionary<string, object>();
+                dict = new Dictionary<string, object?>();
             }
 
             if (!area.IsNullOrWhiteSpace())
             {
-                dict["area"] = area;
+                dict["area"] = area!;
             }
 
-            IDictionary<string, object> values = dict.Aggregate(
-                new ExpandoObject() as IDictionary<string, object>,
+            IDictionary<string, object?> values = dict.Aggregate(
+                new ExpandoObject() as IDictionary<string, object?>,
                 (a, p) =>
                 {
                     a.Add(p.Key, p.Value);
@@ -114,7 +114,7 @@ namespace Umbraco.Extensions
         /// <summary>
         /// Return the Url for an Umbraco controller
         /// </summary>
-        public static string GetUmbracoControllerUrl(this LinkGenerator linkGenerator, string actionName, Type controllerType, IDictionary<string, object> values = null)
+        public static string? GetUmbracoControllerUrl(this LinkGenerator linkGenerator, string actionName, Type controllerType, IDictionary<string, object?>? values = null)
         {
             if (actionName == null)
             {
@@ -148,7 +148,7 @@ namespace Umbraco.Extensions
             return linkGenerator.GetUmbracoControllerUrl(actionName, ControllerExtensions.GetControllerName(controllerType), area, values);
         }
 
-        public static string GetUmbracoApiService<T>(this LinkGenerator linkGenerator, Expression<Func<T, object>> methodSelector)
+        public static string? GetUmbracoApiService<T>(this LinkGenerator linkGenerator, Expression<Func<T, object>> methodSelector)
             where T : UmbracoApiController
         {
             var method = ExpressionHelper.GetMethodInfo(methodSelector);
@@ -159,7 +159,7 @@ namespace Umbraco.Extensions
                     $"Could not find the method {methodSelector} on type {typeof(T)} or the result ");
             }
 
-            if (methodParams.Any() == false)
+            if (methodParams?.Any() == false)
             {
                 return linkGenerator.GetUmbracoApiService<T>(method.Name);
             }
diff --git a/src/Umbraco.Web.Common/Extensions/ModelStateExtensions.cs b/src/Umbraco.Web.Common/Extensions/ModelStateExtensions.cs
index acc2858ece..7509761305 100644
--- a/src/Umbraco.Web.Common/Extensions/ModelStateExtensions.cs
+++ b/src/Umbraco.Web.Common/Extensions/ModelStateExtensions.cs
@@ -14,7 +14,7 @@ namespace Umbraco.Extensions
         /// <param name="prefix"></param>
         /// <returns></returns>
         public static bool IsValid(this ModelStateDictionary state, string prefix) =>
-            state.Where(v => v.Key.StartsWith(prefix + ".")).All(v => !v.Value.Errors.Any());
+            state.Where(v => v.Key.StartsWith(prefix + ".")).All(v => !v.Value?.Errors.Any() ?? false);
 
         public static IDictionary<string, object> ToErrorDictionary(this ModelStateDictionary modelState)
         {
@@ -36,7 +36,7 @@ namespace Umbraco.Extensions
         /// </summary>
         /// <param name="state"></param>
         /// <returns></returns>
-        public static JsonResult ToJsonErrors(this ModelStateDictionary state) =>
+        public static JsonResult? ToJsonErrors(this ModelStateDictionary state) =>
             new JsonResult(new
             {
                 success = state.IsValid.ToString().ToLower(),
@@ -48,7 +48,7 @@ namespace Umbraco.Extensions
                                        name = e.Key,
                                        errors = e.Value.Errors.Select(x => x.ErrorMessage)
                                            .Concat(
-                                               e.Value.Errors.Where(x => x.Exception != null).Select(x => x.Exception.Message))
+                                               e.Value.Errors.Where(x => x.Exception != null).Select(x => x.Exception!.Message))
                                    }
             });
     }
diff --git a/src/Umbraco.Web.Common/Extensions/PublishedContentExtensions.cs b/src/Umbraco.Web.Common/Extensions/PublishedContentExtensions.cs
index 07bad33b50..28ba55c320 100644
--- a/src/Umbraco.Web.Common/Extensions/PublishedContentExtensions.cs
+++ b/src/Umbraco.Web.Common/Extensions/PublishedContentExtensions.cs
@@ -21,14 +21,14 @@ namespace Umbraco.Extensions
         /// </summary>
         /// <param name="content">The content item.</param>
         /// <param name="userService"></param>
-        public static string CreatorName(this IPublishedContent content, IUserService userService) => userService.GetProfileById(content.CreatorId)?.Name;
+        public static string? CreatorName(this IPublishedContent content, IUserService userService) => userService.GetProfileById(content.CreatorId)?.Name;
 
         /// <summary>
         /// Gets the name of the content item writer.
         /// </summary>
         /// <param name="content">The content item.</param>
         /// <param name="userService"></param>
-        public static string WriterName(this IPublishedContent content, IUserService userService) => userService.GetProfileById(content.WriterId)?.Name;
+        public static string? WriterName(this IPublishedContent content, IUserService userService) => userService.GetProfileById(content.WriterId)?.Name;
 
         #endregion
 
@@ -47,7 +47,7 @@ namespace Umbraco.Extensions
         /// one document per culture), and domains, withing the context of a current Uri, assign
         /// a culture to that document.</para>
         /// </remarks>
-        public static string GetCultureFromDomains(this IPublishedContent content, IUmbracoContextAccessor umbracoContextAccessor, ISiteDomainMapper siteDomainHelper, Uri current = null)
+        public static string? GetCultureFromDomains(this IPublishedContent content, IUmbracoContextAccessor umbracoContextAccessor, ISiteDomainMapper siteDomainHelper, Uri? current = null)
         {
             var umbracoContext = umbracoContextAccessor.GetRequiredUmbracoContext();
             return DomainUtilities.GetCultureFromDomains(content.Id, content.Path, current, umbracoContext, siteDomainHelper);
@@ -57,7 +57,7 @@ namespace Umbraco.Extensions
 
         #region Search
 
-        public static IEnumerable<PublishedSearchResult> SearchDescendants(this IPublishedContent content, IExamineManager examineManager, IUmbracoContextAccessor umbracoContextAccessor, string term, string indexName = null)
+        public static IEnumerable<PublishedSearchResult> SearchDescendants(this IPublishedContent content, IExamineManager examineManager, IUmbracoContextAccessor umbracoContextAccessor, string term, string ?indexName = null)
         {
             indexName = string.IsNullOrEmpty(indexName) ? Constants.UmbracoIndexes.ExternalIndexName : indexName;
             if (!examineManager.TryGetIndex(indexName, out var index))
@@ -76,7 +76,7 @@ namespace Umbraco.Extensions
             return query.Execute().ToPublishedSearchResults(umbracoContext.Content);
         }
 
-        public static IEnumerable<PublishedSearchResult> SearchChildren(this IPublishedContent content, IExamineManager examineManager, IUmbracoContextAccessor umbracoContextAccessor, string term, string indexName = null)
+        public static IEnumerable<PublishedSearchResult> SearchChildren(this IPublishedContent content, IExamineManager examineManager, IUmbracoContextAccessor umbracoContextAccessor, string term, string? indexName = null)
         {
             indexName = string.IsNullOrEmpty(indexName) ? Constants.UmbracoIndexes.ExternalIndexName : indexName;
             if (!examineManager.TryGetIndex(indexName, out var index))
diff --git a/src/Umbraco.Web.Common/Extensions/RazorPageExtensions.cs b/src/Umbraco.Web.Common/Extensions/RazorPageExtensions.cs
index d6c3fb5715..41d069919a 100644
--- a/src/Umbraco.Web.Common/Extensions/RazorPageExtensions.cs
+++ b/src/Umbraco.Web.Common/Extensions/RazorPageExtensions.cs
@@ -11,13 +11,13 @@ namespace Umbraco.Extensions
         /// <summary>
         /// Renders a section with default content if the section isn't defined
         /// </summary>
-        public static HtmlString RenderSection(this RazorPage webPage, string name, HtmlString defaultContents)
+        public static HtmlString? RenderSection(this RazorPage webPage, string name, HtmlString defaultContents)
             => webPage.IsSectionDefined(name) ? webPage.RenderSection(name) : defaultContents;
 
         /// <summary>
         /// Renders a section with default content if the section isn't defined
         /// </summary>
-        public static HtmlString RenderSection(this RazorPage webPage, string name, string defaultContents)
+        public static HtmlString? RenderSection(this RazorPage webPage, string name, string defaultContents)
             => webPage.IsSectionDefined(name) ? webPage.RenderSection(name) : new HtmlString(defaultContents);
 
     }
diff --git a/src/Umbraco.Web.Common/Extensions/ServiceCollectionExtensions.cs b/src/Umbraco.Web.Common/Extensions/ServiceCollectionExtensions.cs
index 4441ae6e42..b8de39bb65 100644
--- a/src/Umbraco.Web.Common/Extensions/ServiceCollectionExtensions.cs
+++ b/src/Umbraco.Web.Common/Extensions/ServiceCollectionExtensions.cs
@@ -81,8 +81,8 @@ namespace Umbraco.Extensions
         /// </remarks>
         public static TypeLoader AddTypeLoader(
             this IServiceCollection services,
-            Assembly entryAssembly,
-            IHostingEnvironment hostingEnvironment,
+            Assembly? entryAssembly,
+            IHostingEnvironment? hostingEnvironment,
             ILoggerFactory loggerFactory,
             AppCaches appCaches,
             IConfiguration configuration,
@@ -115,7 +115,7 @@ namespace Umbraco.Extensions
                 typeFinder,
                 runtimeHash,
                 appCaches.RuntimeCache,
-                new DirectoryInfo(hostingEnvironment.LocalTempPath),
+                new DirectoryInfo(hostingEnvironment?.LocalTempPath ?? string.Empty),
                 loggerFactory.CreateLogger<TypeLoader>(),
                 profiler
             );
diff --git a/src/Umbraco.Web.Common/Extensions/UrlHelperExtensions.cs b/src/Umbraco.Web.Common/Extensions/UrlHelperExtensions.cs
index ee45db39c9..237fce8f0a 100644
--- a/src/Umbraco.Web.Common/Extensions/UrlHelperExtensions.cs
+++ b/src/Umbraco.Web.Common/Extensions/UrlHelperExtensions.cs
@@ -27,7 +27,7 @@ namespace Umbraco.Extensions
         /// </summary>
         /// <param name="url"></param>
         /// <returns></returns>
-        public static string GetBackOfficeUrl(this IUrlHelper url)
+        public static string? GetBackOfficeUrl(this IUrlHelper url)
         {
             var backOfficeControllerType = Type.GetType("Umbraco.Web.BackOffice.Controllers");
             if (backOfficeControllerType == null) return "/"; // this would indicate that the installer is installed without the back office
@@ -43,13 +43,13 @@ namespace Umbraco.Extensions
         /// <param name="actionName"></param>
         /// <param name="id"></param>
         /// <returns></returns>
-        public static string GetUmbracoApiService<T>(this IUrlHelper url, UmbracoApiControllerTypeCollection umbracoApiControllerTypeCollection, string actionName, object id = null)
+        public static string? GetUmbracoApiService<T>(this IUrlHelper url, UmbracoApiControllerTypeCollection umbracoApiControllerTypeCollection, string actionName, object? id = null)
             where T : UmbracoApiController
         {
             return url.GetUmbracoApiService(umbracoApiControllerTypeCollection, actionName, typeof(T), id);
         }
 
-        public static string GetUmbracoApiService<T>(this IUrlHelper url, UmbracoApiControllerTypeCollection umbracoApiControllerTypeCollection, Expression<Func<T, object>> methodSelector)
+        public static string? GetUmbracoApiService<T>(this IUrlHelper url, UmbracoApiControllerTypeCollection umbracoApiControllerTypeCollection, Expression<Func<T, object>> methodSelector)
             where T : UmbracoApiController
         {
             var method = ExpressionHelper.GetMethodInfo(methodSelector);
@@ -59,11 +59,11 @@ namespace Umbraco.Extensions
                 throw new MissingMethodException("Could not find the method " + methodSelector + " on type " + typeof(T) + " or the result ");
             }
 
-            if (methodParams.Any() == false)
+            if (methodParams?.Any() == false)
             {
                 return url.GetUmbracoApiService<T>(umbracoApiControllerTypeCollection, method.Name);
             }
-            return url.GetUmbracoApiService<T>(umbracoApiControllerTypeCollection, method.Name, methodParams.Values.First());
+            return url.GetUmbracoApiService<T>(umbracoApiControllerTypeCollection, method.Name, methodParams?.Values.First());
         }
 
         /// <summary>
@@ -75,7 +75,7 @@ namespace Umbraco.Extensions
         /// <param name="apiControllerType"></param>
         /// <param name="id"></param>
         /// <returns></returns>
-        public static string GetUmbracoApiService(this IUrlHelper url, UmbracoApiControllerTypeCollection umbracoApiControllerTypeCollection, string actionName, Type apiControllerType, object id = null)
+        public static string? GetUmbracoApiService(this IUrlHelper url, UmbracoApiControllerTypeCollection umbracoApiControllerTypeCollection, string actionName, Type apiControllerType, object? id = null)
         {
             if (actionName == null) throw new ArgumentNullException(nameof(actionName));
             if (string.IsNullOrWhiteSpace(actionName)) throw new ArgumentException("Value can't be empty or consist only of white-space characters.", nameof(actionName));
@@ -92,7 +92,7 @@ namespace Umbraco.Extensions
                 //set the area to the plugin area
                 area = metaData.AreaName;
             }
-            return url.GetUmbracoApiService(actionName, ControllerExtensions.GetControllerName(apiControllerType), area, id);
+            return url.GetUmbracoApiService(actionName, ControllerExtensions.GetControllerName(apiControllerType), area!, id);
         }
 
         /// <summary>
@@ -103,7 +103,7 @@ namespace Umbraco.Extensions
         /// <param name="controllerName"></param>
         /// <param name="id"></param>
         /// <returns></returns>
-        public static string GetUmbracoApiService(this IUrlHelper url, string actionName, string controllerName, object id = null)
+        public static string? GetUmbracoApiService(this IUrlHelper url, string actionName, string controllerName, object? id = null)
         {
             return url.GetUmbracoApiService(actionName, controllerName, "", id);
         }
@@ -117,7 +117,7 @@ namespace Umbraco.Extensions
         /// <param name="area"></param>
         /// <param name="id"></param>
         /// <returns></returns>
-        public static string GetUmbracoApiService(this IUrlHelper url, string actionName, string controllerName, string area, object id = null)
+        public static string? GetUmbracoApiService(this IUrlHelper url, string actionName, string controllerName, string area, object? id = null)
         {
             if (actionName == null) throw new ArgumentNullException(nameof(actionName));
             if (string.IsNullOrWhiteSpace(actionName)) throw new ArgumentException("Value can't be empty or consist only of white-space characters.", nameof(actionName));
@@ -156,13 +156,13 @@ namespace Umbraco.Extensions
         /// <param name="umbracoApiControllerTypeCollection"></param>
         /// <param name="actionName"></param>
         /// <returns></returns>
-        public static string GetUmbracoApiServiceBaseUrl<T>(this IUrlHelper url, UmbracoApiControllerTypeCollection umbracoApiControllerTypeCollection, string actionName)
+        public static string? GetUmbracoApiServiceBaseUrl<T>(this IUrlHelper url, UmbracoApiControllerTypeCollection umbracoApiControllerTypeCollection, string actionName)
             where T : UmbracoApiController
         {
-            return url.GetUmbracoApiService<T>(umbracoApiControllerTypeCollection, actionName).TrimEnd(actionName);
+            return url.GetUmbracoApiService<T>(umbracoApiControllerTypeCollection, actionName)?.TrimEnd(actionName);
         }
 
-        public static string GetUmbracoApiServiceBaseUrl<T>(this IUrlHelper url, UmbracoApiControllerTypeCollection umbracoApiControllerTypeCollection, Expression<Func<T, object>> methodSelector)
+        public static string? GetUmbracoApiServiceBaseUrl<T>(this IUrlHelper url, UmbracoApiControllerTypeCollection umbracoApiControllerTypeCollection, Expression<Func<T, object>> methodSelector)
             where T : UmbracoApiController
         {
             var method = ExpressionHelper.GetMethodInfo(methodSelector);
@@ -170,7 +170,7 @@ namespace Umbraco.Extensions
             {
                 throw new MissingMethodException("Could not find the method " + methodSelector + " on type " + typeof(T) + " or the result ");
             }
-            return url.GetUmbracoApiService<T>(umbracoApiControllerTypeCollection, method.Name).TrimEnd(method.Name);
+            return url.GetUmbracoApiService<T>(umbracoApiControllerTypeCollection, method.Name)?.TrimEnd(method.Name);
         }
 
         /// <summary>
@@ -219,7 +219,7 @@ namespace Umbraco.Extensions
             return CreateHtmlString(url, htmlEncode);
         }
 
-        private static IHtmlContent CreateHtmlString(string url, bool htmlEncode) => htmlEncode ? new HtmlString(HttpUtility.HtmlEncode(url)) : new HtmlString(url);
+        private static IHtmlContent CreateHtmlString(string? url, bool htmlEncode) => htmlEncode ? new HtmlString(HttpUtility.HtmlEncode(url)) : new HtmlString(url);
 
         public static IHtmlContent GetCropUrl(this IUrlHelper urlHelper, IPublishedContent mediaItem, string propertyAlias, string cropAlias, bool htmlEncode = true, UrlMode urlMode = UrlMode.Default)
         {
@@ -237,14 +237,14 @@ namespace Umbraco.Extensions
             int? width = null,
             int? height = null,
             string propertyAlias = Constants.Conventions.Media.File,
-            string cropAlias = null,
+            string? cropAlias = null,
             int? quality = null,
             ImageCropMode? imageCropMode = null,
             ImageCropAnchor? imageCropAnchor = null,
             bool preferFocalPoint = false,
             bool useCropDimensions = false,
             bool cacheBuster = true,
-            string furtherOptions = null,
+            string? furtherOptions = null,
             bool htmlEncode = true,
             UrlMode urlMode = UrlMode.Default)
         {
@@ -269,14 +269,14 @@ namespace Umbraco.Extensions
             ImageCropAnchor? imageCropAnchor = null,
             bool preferFocalPoint = false,
             bool useCropDimensions = true,
-            string cacheBusterValue = null,
-            string furtherOptions = null,
+            string? cacheBusterValue = null,
+            string? furtherOptions = null,
             bool htmlEncode = true)
         {
             if (imageCropperValue == null) return HtmlString.Empty;
 
             var imageUrl = imageCropperValue.Src;
-            var url = imageUrl.GetCropUrl(imageCropperValue, width, height, cropAlias, quality, imageCropMode,
+            var url = imageUrl?.GetCropUrl(imageCropperValue, width, height, cropAlias, quality, imageCropMode,
                 imageCropAnchor, preferFocalPoint, useCropDimensions, cacheBusterValue, furtherOptions);
 
             return CreateHtmlString(url, htmlEncode);
@@ -302,7 +302,7 @@ namespace Umbraco.Extensions
         /// <param name="controllerName"></param>
         /// <param name="additionalRouteVals"></param>
         /// <returns></returns>
-        public static string SurfaceAction(this IUrlHelper url, IUmbracoContext umbracoContext, IDataProtectionProvider dataProtectionProvider,string action, string controllerName, object additionalRouteVals)
+        public static string SurfaceAction(this IUrlHelper url, IUmbracoContext umbracoContext, IDataProtectionProvider dataProtectionProvider,string action, string controllerName, object? additionalRouteVals)
         {
             return url.SurfaceAction(umbracoContext, dataProtectionProvider, action, controllerName, "", additionalRouteVals);
         }
@@ -316,7 +316,7 @@ namespace Umbraco.Extensions
         /// <param name="area"></param>
         /// <param name="additionalRouteVals"></param>
         /// <returns></returns>
-        public static string SurfaceAction(this IUrlHelper url, IUmbracoContext umbracoContext, IDataProtectionProvider dataProtectionProvider, string action, string controllerName, string area, object additionalRouteVals)
+        public static string SurfaceAction(this IUrlHelper url, IUmbracoContext umbracoContext, IDataProtectionProvider dataProtectionProvider, string action, string controllerName, string area, object? additionalRouteVals)
         {
             if (action == null) throw new ArgumentNullException(nameof(action));
             if (string.IsNullOrEmpty(action)) throw new ArgumentException("Value can't be empty.", nameof(action));
diff --git a/src/Umbraco.Web.Common/Extensions/ViewDataExtensions.cs b/src/Umbraco.Web.Common/Extensions/ViewDataExtensions.cs
index 8e62ca09cf..83754d7e3b 100644
--- a/src/Umbraco.Web.Common/Extensions/ViewDataExtensions.cs
+++ b/src/Umbraco.Web.Common/Extensions/ViewDataExtensions.cs
@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Text;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Mvc.ViewFeatures;
@@ -59,7 +60,7 @@ namespace Umbraco.Extensions
 
             try
             {
-                var decoded = Encoding.UTF8.GetString(Convert.FromBase64String(System.Net.WebUtility.UrlDecode(cookieVal)));
+                var decoded = Encoding.UTF8.GetString(Convert.FromBase64String(System.Net.WebUtility.UrlDecode(cookieVal)!));
                 // deserialize to T and store in viewdata
                 viewData[cookieName] = serializer.Deserialize<T>(decoded);
                 return true;
@@ -70,9 +71,9 @@ namespace Umbraco.Extensions
             }
         }
 
-        public static string GetUmbracoPath(this ViewDataDictionary viewData)
+        public static string? GetUmbracoPath(this ViewDataDictionary viewData)
         {
-            return (string)viewData[TokenUmbracoPath];
+            return (string?)viewData[TokenUmbracoPath];
         }
 
         public static void SetUmbracoPath(this ViewDataDictionary viewData, string value)
@@ -80,9 +81,9 @@ namespace Umbraco.Extensions
             viewData[TokenUmbracoPath] = value;
         }
 
-        public static string GetInstallApiBaseUrl(this ViewDataDictionary viewData)
+        public static string? GetInstallApiBaseUrl(this ViewDataDictionary viewData)
         {
-            return (string)viewData[TokenInstallApiBaseUrl];
+            return (string?)viewData[TokenInstallApiBaseUrl];
         }
 
         public static void SetInstallApiBaseUrl(this ViewDataDictionary viewData, string value)
@@ -90,9 +91,9 @@ namespace Umbraco.Extensions
             viewData[TokenInstallApiBaseUrl] = value;
         }
 
-        public static string GetUmbracoBaseFolder(this ViewDataDictionary viewData)
+        public static string? GetUmbracoBaseFolder(this ViewDataDictionary viewData)
         {
-            return (string)viewData[TokenUmbracoBaseFolder];
+            return (string?)viewData[TokenUmbracoBaseFolder];
         }
 
         public static void SetUmbracoBaseFolder(this ViewDataDictionary viewData, string value)
@@ -104,9 +105,9 @@ namespace Umbraco.Extensions
             viewData[TokenUmbracoVersion] = version;
         }
 
-        public static SemVersion GetUmbracoVersion(this ViewDataDictionary viewData)
+        public static SemVersion? GetUmbracoVersion(this ViewDataDictionary viewData)
         {
-            return (SemVersion) viewData[TokenUmbracoVersion];
+            return (SemVersion?) viewData[TokenUmbracoVersion];
         }
 
         /// <summary>
@@ -114,9 +115,9 @@ namespace Umbraco.Extensions
         /// </summary>
         /// <param name="viewData"></param>
         /// <returns></returns>
-        public static BackOfficeExternalLoginProviderErrors GetExternalSignInProviderErrors(this ViewDataDictionary viewData)
+        public static BackOfficeExternalLoginProviderErrors? GetExternalSignInProviderErrors(this ViewDataDictionary viewData)
         {
-            return (BackOfficeExternalLoginProviderErrors)viewData[TokenExternalSignInError];
+            return (BackOfficeExternalLoginProviderErrors?)viewData[TokenExternalSignInError];
         }
 
         /// <summary>
@@ -129,9 +130,9 @@ namespace Umbraco.Extensions
             viewData[TokenExternalSignInError] = errors;
         }
 
-        public static string GetPasswordResetCode(this ViewDataDictionary viewData)
+        public static string? GetPasswordResetCode(this ViewDataDictionary viewData)
         {
-            return (string)viewData[TokenPasswordResetCode];
+            return (string?)viewData[TokenPasswordResetCode];
         }
 
         public static void SetPasswordResetCode(this ViewDataDictionary viewData, string value)
@@ -144,7 +145,7 @@ namespace Umbraco.Extensions
             viewData[TokenTwoFactorRequired] = providerNames;
         }
 
-        public static bool TryGetTwoFactorProviderNames(this ViewDataDictionary viewData, out IEnumerable<string> providerNames)
+        public static bool TryGetTwoFactorProviderNames(this ViewDataDictionary viewData, [MaybeNullWhen(false)] out IEnumerable<string> providerNames)
         {
             providerNames = viewData[TokenTwoFactorRequired] as IEnumerable<string>;
             return providerNames is not null;
diff --git a/src/Umbraco.Web.Common/Filters/BackOfficeCultureFilter.cs b/src/Umbraco.Web.Common/Filters/BackOfficeCultureFilter.cs
index cf3fe4cf9e..58c934b311 100644
--- a/src/Umbraco.Web.Common/Filters/BackOfficeCultureFilter.cs
+++ b/src/Umbraco.Web.Common/Filters/BackOfficeCultureFilter.cs
@@ -19,7 +19,7 @@ namespace Umbraco.Cms.Web.Common.Filters
 
         public void OnActionExecuting(ActionExecutingContext context)
         {
-            var culture = context.HttpContext.User.Identity.GetCulture();
+            var culture = context.HttpContext.User.Identity?.GetCulture();
             if (culture != null)
             {
                 SetCurrentThreadCulture(culture);
diff --git a/src/Umbraco.Web.Common/Filters/EnsurePartialViewMacroViewContextFilterAttribute.cs b/src/Umbraco.Web.Common/Filters/EnsurePartialViewMacroViewContextFilterAttribute.cs
index e09cc83dd3..ac065b5a92 100644
--- a/src/Umbraco.Web.Common/Filters/EnsurePartialViewMacroViewContextFilterAttribute.cs
+++ b/src/Umbraco.Web.Common/Filters/EnsurePartialViewMacroViewContextFilterAttribute.cs
@@ -90,7 +90,7 @@ namespace Umbraco.Cms.Web.Common.Filters
         {
             public Task RenderAsync(ViewContext context) => Task.CompletedTask;
 
-            public string Path { get; }
+            public string Path { get; } = null!;
         }
     }
 }
diff --git a/src/Umbraco.Web.Common/Filters/ExceptionViewModel.cs b/src/Umbraco.Web.Common/Filters/ExceptionViewModel.cs
index 082f65cfdf..f53fc80d78 100644
--- a/src/Umbraco.Web.Common/Filters/ExceptionViewModel.cs
+++ b/src/Umbraco.Web.Common/Filters/ExceptionViewModel.cs
@@ -4,8 +4,8 @@ namespace Umbraco.Cms.Web.Common.Filters
 {
     public class ExceptionViewModel
     {
-        public string ExceptionMessage { get; set; }
-        public Type ExceptionType { get; set; }
-        public string StackTrace { get; set; }
+        public string? ExceptionMessage { get; set; }
+        public Type? ExceptionType { get; set; }
+        public string? StackTrace { get; set; }
     }
 }
diff --git a/src/Umbraco.Web.Common/Filters/OutgoingNoHyphenGuidFormatAttribute.cs b/src/Umbraco.Web.Common/Filters/OutgoingNoHyphenGuidFormatAttribute.cs
index dd0f78fde1..16613b4289 100644
--- a/src/Umbraco.Web.Common/Filters/OutgoingNoHyphenGuidFormatAttribute.cs
+++ b/src/Umbraco.Web.Common/Filters/OutgoingNoHyphenGuidFormatAttribute.cs
@@ -47,7 +47,7 @@ namespace Umbraco.Cms.Web.Common.Filters
             /// </summary>
             private class GuidNoHyphenConverter : JsonConverter
             {
-                public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
+                public override object ReadJson(JsonReader reader, Type objectType, object? existingValue, JsonSerializer serializer)
                 {
                     switch (reader.TokenType)
                     {
@@ -65,9 +65,9 @@ namespace Umbraco.Cms.Web.Common.Filters
                     }
                 }
 
-                public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
+                public override void WriteJson(JsonWriter writer, object? value, JsonSerializer serializer)
                 {
-                    writer.WriteValue(Guid.Empty.Equals(value) ? Guid.Empty.ToString("N") : ((Guid)value).ToString("N"));
+                    writer.WriteValue(Guid.Empty.Equals(value) ? Guid.Empty.ToString("N") : ((Guid?)value)?.ToString("N"));
                 }
 
                 public override bool CanConvert(Type objectType)
diff --git a/src/Umbraco.Web.Common/Filters/StatusCodeResultAttribute.cs b/src/Umbraco.Web.Common/Filters/StatusCodeResultAttribute.cs
index 98f6d2232c..3ad49c1732 100644
--- a/src/Umbraco.Web.Common/Filters/StatusCodeResultAttribute.cs
+++ b/src/Umbraco.Web.Common/Filters/StatusCodeResultAttribute.cs
@@ -27,7 +27,7 @@ namespace Umbraco.Cms.Web.Common.Filters
 
             httpContext.Response.StatusCode = (int)_statusCode;
 
-            var disableIisCustomErrors = httpContext.RequestServices.GetService<IOptions<WebRoutingSettings>>().Value.TrySkipIisCustomErrors;
+            var disableIisCustomErrors = httpContext.RequestServices.GetService<IOptions<WebRoutingSettings>>()?.Value.TrySkipIisCustomErrors ?? false;
             var statusCodePagesFeature = httpContext.Features.Get<IStatusCodePagesFeature>();
 
             if (statusCodePagesFeature != null)
diff --git a/src/Umbraco.Web.Common/Filters/UmbracoMemberAuthorizeFilter.cs b/src/Umbraco.Web.Common/Filters/UmbracoMemberAuthorizeFilter.cs
index b83f647959..136d2f1c8d 100644
--- a/src/Umbraco.Web.Common/Filters/UmbracoMemberAuthorizeFilter.cs
+++ b/src/Umbraco.Web.Common/Filters/UmbracoMemberAuthorizeFilter.cs
@@ -21,6 +21,9 @@ namespace Umbraco.Cms.Web.Common.Filters
     {
         public UmbracoMemberAuthorizeFilter()
         {
+            AllowType = string.Empty;
+            AllowGroup = string.Empty;
+            AllowMembers = string.Empty;
         }
 
         public  UmbracoMemberAuthorizeFilter(string allowType, string allowGroup, string allowMembers)
diff --git a/src/Umbraco.Web.Common/Filters/UmbracoVirtualPageFilterAttribute.cs b/src/Umbraco.Web.Common/Filters/UmbracoVirtualPageFilterAttribute.cs
index b2b3ed1d39..6c88239abd 100644
--- a/src/Umbraco.Web.Common/Filters/UmbracoVirtualPageFilterAttribute.cs
+++ b/src/Umbraco.Web.Common/Filters/UmbracoVirtualPageFilterAttribute.cs
@@ -24,11 +24,11 @@ namespace Umbraco.Cms.Web.Common.Filters
         /// <inheritdoc/>
         public async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
         {
-            Endpoint endpoint = context.HttpContext.GetEndpoint();
+            Endpoint? endpoint = context.HttpContext.GetEndpoint();
 
             // Check if there is any delegate in the metadata of the route, this
             // will occur when using the ForUmbraco method during routing.
-            CustomRouteContentFinderDelegate contentFinder = endpoint.Metadata.OfType<CustomRouteContentFinderDelegate>().FirstOrDefault();
+            CustomRouteContentFinderDelegate? contentFinder = endpoint?.Metadata.OfType<CustomRouteContentFinderDelegate>().FirstOrDefault();
 
             if (contentFinder != null)
             {
diff --git a/src/Umbraco.Web.Common/Filters/ValidateUmbracoFormRouteStringAttribute.cs b/src/Umbraco.Web.Common/Filters/ValidateUmbracoFormRouteStringAttribute.cs
index 0c51edd4e1..3337f74a4e 100644
--- a/src/Umbraco.Web.Common/Filters/ValidateUmbracoFormRouteStringAttribute.cs
+++ b/src/Umbraco.Web.Common/Filters/ValidateUmbracoFormRouteStringAttribute.cs
@@ -51,14 +51,14 @@ namespace Umbraco.Cms.Web.Common.Filters
 
             }
 
-            public void ValidateRouteString(string ufprt, string currentController, string currentAction, string currentArea)
+            public void ValidateRouteString(string? ufprt, string currentController, string currentAction, string? currentArea)
             {
                 if (ufprt.IsNullOrWhiteSpace())
                 {
                     throw new HttpUmbracoFormRouteStringException("The required request field \"ufprt\" is not present.");
                 }
 
-                if (!EncryptionHelper.DecryptAndValidateEncryptedRouteString(_dataProtectionProvider, ufprt, out var additionalDataParts))
+                if (!EncryptionHelper.DecryptAndValidateEncryptedRouteString(_dataProtectionProvider, ufprt!, out var additionalDataParts))
                 {
                     throw new HttpUmbracoFormRouteStringException("The Umbraco form request route string could not be decrypted.");
                 }
diff --git a/src/Umbraco.Web.Common/IUmbracoHelperAccessor.cs b/src/Umbraco.Web.Common/IUmbracoHelperAccessor.cs
index b2085bc175..b170546005 100644
--- a/src/Umbraco.Web.Common/IUmbracoHelperAccessor.cs
+++ b/src/Umbraco.Web.Common/IUmbracoHelperAccessor.cs
@@ -1,7 +1,9 @@
+using System.Diagnostics.CodeAnalysis;
+
 namespace Umbraco.Cms.Web.Common
 {
     public interface IUmbracoHelperAccessor
     {
-        bool TryGetUmbracoHelper(out UmbracoHelper umbracoHelper);
+        bool TryGetUmbracoHelper([MaybeNullWhen(false)] out UmbracoHelper umbracoHelper);
     }
 }
diff --git a/src/Umbraco.Web.Common/Localization/UmbracoBackOfficeIdentityCultureProvider.cs b/src/Umbraco.Web.Common/Localization/UmbracoBackOfficeIdentityCultureProvider.cs
index 96022cdcc7..fbe0aaacb5 100644
--- a/src/Umbraco.Web.Common/Localization/UmbracoBackOfficeIdentityCultureProvider.cs
+++ b/src/Umbraco.Web.Common/Localization/UmbracoBackOfficeIdentityCultureProvider.cs
@@ -24,9 +24,9 @@ namespace Umbraco.Cms.Web.Common.Localization
         public UmbracoBackOfficeIdentityCultureProvider(RequestLocalizationOptions localizationOptions) => _localizationOptions = localizationOptions;
 
         /// <inheritdoc/>
-        public override Task<ProviderCultureResult> DetermineProviderCultureResult(HttpContext httpContext)
+        public override Task<ProviderCultureResult?> DetermineProviderCultureResult(HttpContext httpContext)
         {
-            CultureInfo culture = httpContext.User.Identity.GetCulture();
+            CultureInfo? culture = httpContext.User.Identity?.GetCulture();
 
             if (culture is null)
             {
@@ -37,23 +37,23 @@ namespace Umbraco.Cms.Web.Common.Localization
             {
                 // We need to dynamically change the supported cultures since we won't ever know what languages are used since
                 // they are dynamic within Umbraco. We have to handle this for both UI and Region cultures, in case people run different region and UI languages
-                var cultureExists = _localizationOptions.SupportedCultures.Contains(culture);
+                var cultureExists = _localizationOptions.SupportedCultures?.Contains(culture) ?? false;
 
                 if (!cultureExists)
                 {
                     // add this as a supporting culture
-                    _localizationOptions.SupportedCultures.Add(culture);
+                    _localizationOptions.SupportedCultures?.Add(culture);
                 }
 
-                var uiCultureExists = _localizationOptions.SupportedCultures.Contains(culture);
+                var uiCultureExists = _localizationOptions.SupportedCultures?.Contains(culture) ?? false;
 
                 if (!uiCultureExists)
                 {
                     // add this as a supporting culture
-                    _localizationOptions.SupportedUICultures.Add(culture);
+                    _localizationOptions.SupportedUICultures?.Add(culture);
                 }
 
-                return Task.FromResult(new ProviderCultureResult(culture.Name));
+                return Task.FromResult<ProviderCultureResult?>(new ProviderCultureResult(culture.Name));
             }
         }
     }
diff --git a/src/Umbraco.Web.Common/Localization/UmbracoPublishedContentCultureProvider.cs b/src/Umbraco.Web.Common/Localization/UmbracoPublishedContentCultureProvider.cs
index 50e8d859ea..64ce9a6f8e 100644
--- a/src/Umbraco.Web.Common/Localization/UmbracoPublishedContentCultureProvider.cs
+++ b/src/Umbraco.Web.Common/Localization/UmbracoPublishedContentCultureProvider.cs
@@ -25,12 +25,12 @@ namespace Umbraco.Cms.Web.Common.Localization
         public UmbracoPublishedContentCultureProvider(RequestLocalizationOptions localizationOptions) => _localizationOptions = localizationOptions;
 
         /// <inheritdoc/>
-        public override Task<ProviderCultureResult> DetermineProviderCultureResult(HttpContext httpContext)
+        public override Task<ProviderCultureResult?> DetermineProviderCultureResult(HttpContext httpContext)
         {
-            UmbracoRouteValues routeValues = httpContext.Features.Get<UmbracoRouteValues>();
+            UmbracoRouteValues? routeValues = httpContext.Features.Get<UmbracoRouteValues>();
             if (routeValues != null)
             {
-                string culture = routeValues.PublishedRequest?.Culture;
+                string? culture = routeValues.PublishedRequest?.Culture;
                 if (culture != null)
                 {
                     lock (_locker)
@@ -39,28 +39,28 @@ namespace Umbraco.Cms.Web.Common.Localization
                         // they are dynamic within Umbraco. We have to handle this for both UI and Region cultures, in case people run different region and UI languages
                         // This code to check existence is borrowed from aspnetcore to avoid creating a CultureInfo
                         // https://github.com/dotnet/aspnetcore/blob/b795ac3546eb3e2f47a01a64feb3020794ca33bb/src/Middleware/Localization/src/RequestLocalizationMiddleware.cs#L165
-                        CultureInfo existingCulture = _localizationOptions.SupportedCultures.FirstOrDefault(supportedCulture =>
+                        CultureInfo? existingCulture = _localizationOptions.SupportedCultures?.FirstOrDefault(supportedCulture =>
                             StringSegment.Equals(supportedCulture.Name, culture, StringComparison.OrdinalIgnoreCase));
 
                         if (existingCulture == null)
                         {
                             // add this as a supporting culture
                             var ci = CultureInfo.GetCultureInfo(culture);
-                            _localizationOptions.SupportedCultures.Add(ci);
+                            _localizationOptions.SupportedCultures?.Add(ci);
                         }
 
-                        CultureInfo existingUICulture = _localizationOptions.SupportedUICultures.FirstOrDefault(supportedCulture =>
+                        CultureInfo? existingUICulture = _localizationOptions.SupportedUICultures?.FirstOrDefault(supportedCulture =>
                             StringSegment.Equals(supportedCulture.Name, culture, StringComparison.OrdinalIgnoreCase));
 
                         if (existingUICulture == null)
                         {
                             // add this as a supporting culture
                             var ci = CultureInfo.GetCultureInfo(culture);
-                            _localizationOptions.SupportedUICultures.Add(ci);
+                            _localizationOptions.SupportedUICultures?.Add(ci);
                         }
                     }
 
-                    return Task.FromResult(new ProviderCultureResult(culture));
+                    return Task.FromResult<ProviderCultureResult?>(new ProviderCultureResult(culture));
                 }
             }
 
diff --git a/src/Umbraco.Web.Common/Macros/MacroRenderer.cs b/src/Umbraco.Web.Common/Macros/MacroRenderer.cs
index 3a80e555c3..3c4bebc9c4 100644
--- a/src/Umbraco.Web.Common/Macros/MacroRenderer.cs
+++ b/src/Umbraco.Web.Common/Macros/MacroRenderer.cs
@@ -108,14 +108,14 @@ namespace Umbraco.Cms.Web.Common.Macros
             }
 
             foreach (var value in model.Properties.Select(x => x.Value))
-                id.AppendFormat("{0}-", value.Length <= 255 ? value : value.Substring(0, 255));
+                id.AppendFormat("{0}-", value?.Length <= 255 ? value : value?.Substring(0, 255));
 
             return id.ToString();
         }
 
         // gets this macro content from the cache
         // ensuring that it is appropriate to use the cache
-        private MacroContent GetMacroContentFromCache(MacroModel model)
+        private MacroContent? GetMacroContentFromCache(MacroModel model)
         {
             if (!_umbracoContextAccessor.TryGetUmbracoContext(out var umbracoContext))
             {
@@ -170,8 +170,8 @@ namespace Umbraco.Cms.Web.Common.Macros
             // do not cache if it should cache by member and there's not member
             if (model.CacheByMember)
             {
-                var memberManager = _httpContextAccessor.HttpContext.RequestServices.GetRequiredService<IMemberManager>();
-                var member = await memberManager.GetCurrentMemberAsync();
+                var memberManager = _httpContextAccessor.HttpContext?.RequestServices.GetRequiredService<IMemberManager>();
+                MemberIdentityUser? member = await memberManager?.GetCurrentMemberAsync()!;
                 if (member is null)
                 {
                     return;
@@ -193,16 +193,16 @@ namespace Umbraco.Cms.Web.Common.Macros
 
         // gets the macro source file name
         // null if the macro is not file-based, or not supported
-        internal static string GetMacroFileName(MacroModel model)
+        internal static string? GetMacroFileName(MacroModel model)
         {
-            string filename = model.MacroSource; // partial views are saved with their full virtual path
+            string? filename = model.MacroSource; // partial views are saved with their full virtual path
 
             return string.IsNullOrEmpty(filename) ? null : filename;
         }
 
         // gets the macro source file
         // null if macro is not file-based
-        private FileInfo GetMacroFile(MacroModel model)
+        private FileInfo? GetMacroFile(MacroModel model)
         {
             var filename = GetMacroFileName(model);
             if (filename == null)
@@ -217,7 +217,7 @@ namespace Umbraco.Cms.Web.Common.Macros
         }
 
         // updates the model properties values according to the attributes
-        private static void UpdateMacroModelProperties(MacroModel model, IDictionary<string, object> macroParams)
+        private static void UpdateMacroModelProperties(MacroModel model, IDictionary<string, object?>? macroParams)
         {
             foreach (var prop in model.Properties)
             {
@@ -231,7 +231,7 @@ namespace Umbraco.Cms.Web.Common.Macros
 
         #region Render/Execute
 
-        public async Task<MacroContent> RenderAsync(string macroAlias, IPublishedContent content, IDictionary<string, object> macroParams)
+        public async Task<MacroContent> RenderAsync(string macroAlias, IPublishedContent? content, IDictionary<string, object?>? macroParams)
         {
             var m = _appCaches.RuntimeCache.GetCacheItem(CacheKeys.MacroFromAliasCacheKey + macroAlias, () => _macroService.GetByAlias(macroAlias));
 
@@ -244,7 +244,7 @@ namespace Umbraco.Cms.Web.Common.Macros
             return await RenderAsync(macro, content);
         }
 
-        private async Task<MacroContent> RenderAsync(MacroModel macro, IPublishedContent content)
+        private async Task<MacroContent> RenderAsync(MacroModel macro, IPublishedContent? content)
         {
             if (content == null)
                 throw new ArgumentNullException(nameof(content));
@@ -294,7 +294,7 @@ namespace Umbraco.Cms.Web.Common.Macros
         /// <summary>
         /// Executes a macro of a given type.
         /// </summary>
-        private Attempt<MacroContent> ExecuteMacroWithErrorWrapper(MacroModel macro, string msgIn, string msgOut, Func<MacroContent> getMacroContent, Func<string> msgErr)
+        private Attempt<MacroContent?> ExecuteMacroWithErrorWrapper(MacroModel macro, string msgIn, string msgOut, Func<MacroContent> getMacroContent, Func<string> msgErr)
         {
             using (_profilingLogger.DebugDuration<MacroRenderer>(msgIn, msgOut))
             {
@@ -305,7 +305,7 @@ namespace Umbraco.Cms.Web.Common.Macros
         /// <summary>
         /// Executes a macro of a given type.
         /// </summary>
-        private Attempt<MacroContent> ExecuteProfileMacroWithErrorWrapper(MacroModel macro, string msgIn, Func<MacroContent> getMacroContent, Func<string> msgErr)
+        private Attempt<MacroContent?> ExecuteProfileMacroWithErrorWrapper(MacroModel macro, string msgIn, Func<MacroContent> getMacroContent, Func<string> msgErr)
         {
             try
             {
@@ -350,7 +350,7 @@ namespace Umbraco.Cms.Web.Common.Macros
         /// <remarks>Returns an attempt that is successful if the macro ran successfully. If the macro failed
         /// to run properly, the attempt fails, though it may contain a content. But for instance that content
         /// should not be cached. In that case the attempt may also contain an exception.</remarks>
-        private Attempt<MacroContent> ExecuteMacroOfType(MacroModel model, IPublishedContent content)
+        private Attempt<MacroContent?> ExecuteMacroOfType(MacroModel model, IPublishedContent content)
         {
             if (model == null)
             {
@@ -380,8 +380,12 @@ namespace Umbraco.Cms.Web.Common.Macros
 
         // parses attribute value looking for [@requestKey], [%sessionKey]
         // supports fallbacks eg "[@requestKey],[%sessionKey],1234"
-        private string ParseAttribute(string attributeValue)
+        private string? ParseAttribute(string? attributeValue)
         {
+            if (attributeValue is null)
+            {
+                return attributeValue;
+            }
             // check for potential querystring/cookie variables
             attributeValue = attributeValue.Trim();
             if (attributeValue.StartsWith("[") == false)
diff --git a/src/Umbraco.Web.Common/Macros/PartialViewMacroEngine.cs b/src/Umbraco.Web.Common/Macros/PartialViewMacroEngine.cs
index 0b60de97cb..072ebf78a3 100644
--- a/src/Umbraco.Web.Common/Macros/PartialViewMacroEngine.cs
+++ b/src/Umbraco.Web.Common/Macros/PartialViewMacroEngine.cs
@@ -59,11 +59,11 @@ namespace Umbraco.Cms.Web.Common.Macros
             }
 
             HttpContext httpContext = _httpContextAccessor.GetRequiredHttpContext();
-            
+
             RouteData currentRouteData = httpContext.GetRouteData();
 
             // Check if there's proxied ViewData (i.e. returned from a SurfaceController)
-            ProxyViewDataFeature proxyViewDataFeature = httpContext.Features.Get<ProxyViewDataFeature>();
+            ProxyViewDataFeature? proxyViewDataFeature = httpContext.Features.Get<ProxyViewDataFeature>();
             ViewDataDictionary viewData = proxyViewDataFeature?.ViewData ?? new ViewDataDictionary(_modelMetadataProvider, new ModelStateDictionary());
             ITempDataDictionary tempData = proxyViewDataFeature?.TempData ?? _tempDataDictionaryFactory.GetTempData(httpContext);
 
@@ -79,7 +79,7 @@ namespace Umbraco.Cms.Web.Common.Macros
             var writer = new StringWriter();
             var viewComponentContext = new ViewComponentContext(
                 new ViewComponentDescriptor(),
-                new Dictionary<string, object>(),
+                new Dictionary<string, object?>(),
                 HtmlEncoder.Default,
                 viewContext,
                 writer);
diff --git a/src/Umbraco.Web.Common/Macros/PartialViewMacroViewComponent.cs b/src/Umbraco.Web.Common/Macros/PartialViewMacroViewComponent.cs
index 5cab93c00f..8afefc9d16 100644
--- a/src/Umbraco.Web.Common/Macros/PartialViewMacroViewComponent.cs
+++ b/src/Umbraco.Web.Common/Macros/PartialViewMacroViewComponent.cs
@@ -38,7 +38,7 @@ namespace Umbraco.Cms.Web.Common.Macros
                 _macro.Id,
                 _macro.Alias,
                 _macro.Name,
-                _macro.Properties.ToDictionary(x => x.Key, x => (object)x.Value));
+                _macro.Properties.ToDictionary(x => x.Key, x => (object?)x.Value));
 
             ViewViewComponentResult result =  View(_macro.MacroSource, model);
 
diff --git a/src/Umbraco.Web.Common/Middleware/PreviewAuthenticationMiddleware.cs b/src/Umbraco.Web.Common/Middleware/PreviewAuthenticationMiddleware.cs
index 50338f70e3..84b4991b96 100644
--- a/src/Umbraco.Web.Common/Middleware/PreviewAuthenticationMiddleware.cs
+++ b/src/Umbraco.Web.Common/Middleware/PreviewAuthenticationMiddleware.cs
@@ -49,7 +49,7 @@ namespace Umbraco.Cms.Web.Common.Middleware
                     // If we've gotten this far it means a preview cookie has been set and a front-end umbraco document request is executing.
                     // In this case, authentication will not have occurred for an Umbraco back office User, however we need to perform the authentication
                     // for the user here so that the preview capability can be authorized otherwise only the non-preview page will be rendered.
-                    if (request.Cookies.TryGetValue(cookieOptions.Cookie.Name, out var cookie))
+                    if (cookieOptions.Cookie.Name is not null && request.Cookies.TryGetValue(cookieOptions.Cookie.Name, out var cookie))
                     {
                         var unprotected = cookieOptions.TicketDataFormat.Unprotect(cookie);
                         var backOfficeIdentity = unprotected?.Principal.GetUmbracoIdentity();
@@ -58,7 +58,7 @@ namespace Umbraco.Cms.Web.Common.Middleware
                             // Ok, we've got a real ticket, now we can add this ticket's identity to the current
                             // Principal, this means we'll have 2 identities assigned to the principal which we can
                             // use to authorize the preview and allow for a back office User.
-                            context.User.AddIdentity(backOfficeIdentity);
+                            context.User?.AddIdentity(backOfficeIdentity);
                         }
                     }
 
diff --git a/src/Umbraco.Web.Common/Middleware/UmbracoRequestMiddleware.cs b/src/Umbraco.Web.Common/Middleware/UmbracoRequestMiddleware.cs
index b03528ec46..be83e15a4b 100644
--- a/src/Umbraco.Web.Common/Middleware/UmbracoRequestMiddleware.cs
+++ b/src/Umbraco.Web.Common/Middleware/UmbracoRequestMiddleware.cs
@@ -51,7 +51,7 @@ namespace Umbraco.Cms.Web.Common.Middleware
         private readonly IVariationContextAccessor _variationContextAccessor;
         private readonly IDefaultCultureAccessor _defaultCultureAccessor;
         private SmidgeOptions _smidgeOptions;
-        private readonly WebProfiler _profiler;
+        private readonly WebProfiler? _profiler;
 
 #pragma warning disable IDE0044 // Add readonly modifier
         private static bool s_firstBackOfficeRequest;
@@ -111,7 +111,7 @@ namespace Umbraco.Cms.Web.Common.Middleware
             _variationContextAccessor.VariationContext ??= new VariationContext(_defaultCultureAccessor.DefaultCulture);
             UmbracoContextReference umbracoContextReference = _umbracoContextFactory.EnsureUmbracoContext();
 
-            Uri currentApplicationUrl = GetApplicationUrlFromCurrentRequest(context.Request);
+            Uri? currentApplicationUrl = GetApplicationUrlFromCurrentRequest(context.Request);
             _hostingEnvironment.EnsureApplicationMainUrl(currentApplicationUrl);
 
             var pathAndQuery = context.Request.GetEncodedPathAndQuery();
@@ -181,8 +181,8 @@ namespace Umbraco.Cms.Web.Common.Middleware
             }
 
             if (_umbracoRequestPaths.IsBackOfficeRequest(absPath)
-                || absPath.Value.InvariantStartsWith($"/{_smidgeOptions.UrlOptions.CompositeFilePath}")
-                || absPath.Value.InvariantStartsWith($"/{_smidgeOptions.UrlOptions.BundleFilePath}"))
+                || (absPath.Value?.InvariantStartsWith($"/{_smidgeOptions.UrlOptions.CompositeFilePath}") ?? false)
+                || (absPath.Value?.InvariantStartsWith($"/{_smidgeOptions.UrlOptions.BundleFilePath}") ?? false))
             {
                 LazyInitializer.EnsureInitialized(ref s_firstBackOfficeRequest, ref s_firstBackOfficeReqestFlag, ref s_firstBackOfficeRequestLocker, () =>
                 {
@@ -192,7 +192,7 @@ namespace Umbraco.Cms.Web.Common.Middleware
             }
         }
 
-        private Uri GetApplicationUrlFromCurrentRequest(HttpRequest request)
+        private Uri? GetApplicationUrlFromCurrentRequest(HttpRequest request)
         {
             // We only consider GET and POST.
             // Especially the DEBUG sent when debugging the application is annoying because it uses http, even when the https is available.
diff --git a/src/Umbraco.Web.Common/ModelBinders/ContentModelBinder.cs b/src/Umbraco.Web.Common/ModelBinders/ContentModelBinder.cs
index 21a6af1723..6cc20f4f52 100644
--- a/src/Umbraco.Web.Common/ModelBinders/ContentModelBinder.cs
+++ b/src/Umbraco.Web.Common/ModelBinders/ContentModelBinder.cs
@@ -32,7 +32,7 @@ namespace Umbraco.Cms.Web.Common.ModelBinders
             // only IPublishedContent will ever exist in the request so when this model binder is used as an IModelBinder
             // in the aspnet pipeline it will really only support converting from IPublishedContent which is contained
             // in the UmbracoRouteValues --> IContentModel
-            UmbracoRouteValues umbracoRouteValues = bindingContext.HttpContext.Features.Get<UmbracoRouteValues>();
+            UmbracoRouteValues? umbracoRouteValues = bindingContext.HttpContext.Features.Get<UmbracoRouteValues>();
             if (umbracoRouteValues is null)
             {
                 return Task.CompletedTask;
@@ -53,7 +53,7 @@ namespace Umbraco.Cms.Web.Common.ModelBinders
         /// <summary>
         /// Attempts to bind the model
         /// </summary>
-        public void BindModel(ModelBindingContext bindingContext, object source, Type modelType)
+        public void BindModel(ModelBindingContext bindingContext, object? source, Type modelType)
         {
             // Null model, return
             if (source == null)
@@ -124,7 +124,7 @@ namespace Umbraco.Cms.Web.Common.ModelBinders
             }
 
             // Last chance : try to convert
-            Attempt<object> attempt2 = source.TryConvertTo(modelType);
+            Attempt<object?> attempt2 = source.TryConvertTo(modelType);
             if (attempt2.Success)
             {
                 bindingContext.Result = ModelBindingResult.Success(attempt2.Result);
diff --git a/src/Umbraco.Web.Common/ModelBinders/ContentModelBinderProvider.cs b/src/Umbraco.Web.Common/ModelBinders/ContentModelBinderProvider.cs
index 1e07d05985..5fe1638394 100644
--- a/src/Umbraco.Web.Common/ModelBinders/ContentModelBinderProvider.cs
+++ b/src/Umbraco.Web.Common/ModelBinders/ContentModelBinderProvider.cs
@@ -10,7 +10,7 @@ namespace Umbraco.Cms.Web.Common.ModelBinders
     /// </summary>
     public class ContentModelBinderProvider : IModelBinderProvider
     {
-        public IModelBinder GetBinder(ModelBinderProviderContext context)
+        public IModelBinder? GetBinder(ModelBinderProviderContext context)
         {
             var modelType = context.Metadata.ModelType;
 
diff --git a/src/Umbraco.Web.Common/Models/LoginModel.cs b/src/Umbraco.Web.Common/Models/LoginModel.cs
index 07bcf8b7ce..304953a925 100644
--- a/src/Umbraco.Web.Common/Models/LoginModel.cs
+++ b/src/Umbraco.Web.Common/Models/LoginModel.cs
@@ -7,13 +7,13 @@ namespace Umbraco.Cms.Web.Common.Models
     {
         [Required]
         [Display(Name = "User name")]
-        public string Username { get; set; }
+        public string Username { get; set; } = null!;
 
         [Required]
         [DataType(DataType.Password)]
         [Display(Name = "Password")]
         [StringLength(maximumLength: 256)]
-        public string Password { get; set; }
+        public string Password { get; set; } = null!;
 
         [Display(Name = "Remember me?")]
         public bool RememberMe { get; set; }
diff --git a/src/Umbraco.Web.Common/Models/PostRedirectModel.cs b/src/Umbraco.Web.Common/Models/PostRedirectModel.cs
index ac12a12f0b..a9b929282d 100644
--- a/src/Umbraco.Web.Common/Models/PostRedirectModel.cs
+++ b/src/Umbraco.Web.Common/Models/PostRedirectModel.cs
@@ -10,6 +10,6 @@ namespace Umbraco.Cms.Web.Common.Models
         /// The path to redirect to when update is successful, if not specified then the user will be
         /// redirected to the current Umbraco page
         /// </summary>
-        public string RedirectUrl { get; set; }
+        public string? RedirectUrl { get; set; }
     }
 }
diff --git a/src/Umbraco.Web.Common/ModelsBuilder/InMemoryModelFactory.cs b/src/Umbraco.Web.Common/ModelsBuilder/InMemoryModelFactory.cs
index 5019bbb4e3..cdf3d774c2 100644
--- a/src/Umbraco.Web.Common/ModelsBuilder/InMemoryModelFactory.cs
+++ b/src/Umbraco.Web.Common/ModelsBuilder/InMemoryModelFactory.cs
@@ -34,12 +34,12 @@ namespace Umbraco.Cms.Web.Common.ModelsBuilder
         private bool _pendingRebuild;
         private readonly IProfilingLogger _profilingLogger;
         private readonly ILogger<InMemoryModelFactory> _logger;
-        private readonly FileSystemWatcher _watcher;
+        private readonly FileSystemWatcher? _watcher;
         private int _ver;
-        private int _skipver;
+        private int? _skipver;
         private readonly int _debugLevel;
-        private RoslynCompiler _roslynCompiler;
-        private UmbracoAssemblyLoadContext _currentAssemblyLoadContext;
+        private RoslynCompiler? _roslynCompiler;
+        private UmbracoAssemblyLoadContext? _currentAssemblyLoadContext;
         private readonly Lazy<UmbracoServices> _umbracoServices; // fixme: this is because of circular refs :(
         private static readonly Regex s_assemblyVersionRegex = new Regex("AssemblyVersion\\(\"[0-9]+.[0-9]+.[0-9]+.[0-9]+\"\\)", RegexOptions.Compiled);
         private static readonly string[] s_ourFiles = { "models.hash", "models.generated.cs", "all.generated.cs", "all.dll.path", "models.err", "Compiled" };
@@ -51,7 +51,7 @@ namespace Umbraco.Cms.Web.Common.ModelsBuilder
         private readonly ApplicationPartManager _applicationPartManager;
         private static readonly Regex s_usingRegex = new Regex("^using(.*);", RegexOptions.Compiled | RegexOptions.Multiline);
         private static readonly Regex s_aattrRegex = new Regex("^\\[assembly:(.*)\\]", RegexOptions.Compiled | RegexOptions.Multiline);
-        private readonly Lazy<string> _pureLiveDirectory;
+        private readonly Lazy<string> _pureLiveDirectory = null!;
         private bool _disposedValue;
 
 
@@ -103,7 +103,7 @@ namespace Umbraco.Cms.Web.Common.ModelsBuilder
             AssemblyLoadContext.Default.Resolving += OnResolvingDefaultAssemblyLoadContext;
         }
 
-        public event EventHandler ModelsChanged;
+        public event EventHandler? ModelsChanged;
 
         private UmbracoServices UmbracoServices => _umbracoServices.Value;
 
@@ -113,7 +113,7 @@ namespace Umbraco.Cms.Web.Common.ModelsBuilder
         /// <remarks>
         /// Can be null
         /// </remarks>
-        public Assembly CurrentModelsAssembly { get; private set; }
+        public Assembly? CurrentModelsAssembly { get; private set; }
 
         /// <inheritdoc />
         public object SyncRoot { get; } = new object();
@@ -145,7 +145,7 @@ namespace Umbraco.Cms.Web.Common.ModelsBuilder
         /// This is required because the razor engine will only try to load things from the default context, it doesn't know anything
         /// about our context so we need to proxy.
         /// </remarks>
-        private Assembly OnResolvingDefaultAssemblyLoadContext(AssemblyLoadContext assemblyLoadContext, AssemblyName assemblyName)
+        private Assembly? OnResolvingDefaultAssemblyLoadContext(AssemblyLoadContext assemblyLoadContext, AssemblyName assemblyName)
             => assemblyName.Name == RoslynCompiler.GeneratedAssemblyName
                 ? _currentAssemblyLoadContext?.LoadFromAssemblyName(assemblyName)
                 : null;
@@ -153,7 +153,7 @@ namespace Umbraco.Cms.Web.Common.ModelsBuilder
         public IPublishedElement CreateModel(IPublishedElement element)
         {
             // get models, rebuilding them if needed
-            Dictionary<string, ModelInfo> infos = EnsureModels()?.ModelInfos;
+            Dictionary<string, ModelInfo>? infos = EnsureModels()?.ModelInfos;
             if (infos == null)
             {
                 return element;
@@ -166,7 +166,7 @@ namespace Umbraco.Cms.Web.Common.ModelsBuilder
             infos.TryGetValue(contentTypeAlias, out var info);
 
             // create model
-            return info == null ? element : info.Ctor(element, _publishedValueFallback);
+            return info is null || info.Ctor is null ? element : info.Ctor(element, _publishedValueFallback);
         }
 
         // this runs only once the factory is ready
@@ -179,30 +179,36 @@ namespace Umbraco.Cms.Web.Common.ModelsBuilder
 
         // this runs only once the factory is ready
         // NOT when building models
-        public IList CreateModelList(string alias)
+        public IList CreateModelList(string? alias)
         {
             Infos infos = EnsureModels();
 
             // fail fast
-            if (infos == null)
+            if (infos is null || alias is null)
             {
                 return new List<IPublishedElement>();
             }
 
-            if (!infos.ModelInfos.TryGetValue(alias, out ModelInfo modelInfo))
+            if (infos.ModelInfos is null || !infos.ModelInfos.TryGetValue(alias, out ModelInfo? modelInfo))
             {
                 return new List<IPublishedElement>();
             }
 
-            Func<IList> ctor = modelInfo.ListCtor;
+            Func<IList>? ctor = modelInfo.ListCtor;
             if (ctor != null)
             {
                 return ctor();
             }
 
+            if (modelInfo.ModelType is null)
+            {
+                return new List<IPublishedElement>();
+            }
+
             Type listType = typeof(List<>).MakeGenericType(modelInfo.ModelType);
             ctor = modelInfo.ListCtor = ReflectionUtilities.EmitConstructor<Func<IList>>(declaring: listType);
-            return ctor();
+
+            return ctor is null ? new List<IPublishedElement>() : ctor();
         }
 
         /// <inheritdoc />
@@ -360,7 +366,7 @@ namespace Umbraco.Cms.Web.Common.ModelsBuilder
                 _currentAssemblyLoadContext.Unload();
 
                 // we need to remove the current part too
-                ApplicationPart currentPart = _applicationPartManager.ApplicationParts.FirstOrDefault(x => x.Name == RoslynCompiler.GeneratedAssemblyName);
+                ApplicationPart? currentPart = _applicationPartManager.ApplicationParts.FirstOrDefault(x => x.Name == RoslynCompiler.GeneratedAssemblyName);
                 if (currentPart != null)
                 {
                     _applicationPartManager.ApplicationParts.Remove(currentPart);
@@ -454,14 +460,14 @@ namespace Umbraco.Cms.Web.Common.ModelsBuilder
                     {
                         assembly = ReloadAssembly(dllPath);
 
-                        ModelsBuilderAssemblyAttribute attr = assembly.GetCustomAttribute<ModelsBuilderAssemblyAttribute>();
+                        ModelsBuilderAssemblyAttribute? attr = assembly.GetCustomAttribute<ModelsBuilderAssemblyAttribute>();
                         if (attr != null && attr.IsInMemory && attr.SourceHash == currentHash)
                         {
                             // if we were to resume at that revision, then _ver would keep increasing
                             // and that is probably a bad idea - so, we'll always rebuild starting at
                             // ver 1, but we remember we want to skip that one - so we never end up
                             // with the "same but different" version of the assembly in memory
-                            _skipver = assembly.GetName().Version.Revision;
+                            _skipver = assembly.GetName().Version?.Revision;
 
                             _logger.LogDebug("Loading cached models (dll).");
                             return assembly;
@@ -561,8 +567,13 @@ namespace Umbraco.Cms.Web.Common.ModelsBuilder
             if (File.Exists(dllPathFile))
             {
                 var dllPath = File.ReadAllText(dllPathFile);
-                DirectoryInfo dirInfo = new DirectoryInfo(dllPath).Parent;
-                IEnumerable<FileInfo> files = dirInfo.GetFiles().Where(f => f.FullName != dllPath);
+                DirectoryInfo? dirInfo = new DirectoryInfo(dllPath).Parent;
+                IEnumerable<FileInfo>? files = dirInfo?.GetFiles().Where(f => f.FullName != dllPath);
+                if (files is null)
+                {
+                    return;
+                }
+
                 foreach (FileInfo file in files)
                 {
                     try
@@ -626,8 +637,8 @@ namespace Umbraco.Cms.Web.Common.ModelsBuilder
 
             foreach (Type type in types)
             {
-                ConstructorInfo constructor = null;
-                Type parameterType = null;
+                ConstructorInfo? constructor = null;
+                Type? parameterType = null;
 
                 foreach (ConstructorInfo ctor in type.GetConstructors())
                 {
@@ -649,12 +660,12 @@ namespace Umbraco.Cms.Web.Common.ModelsBuilder
                     throw new InvalidOperationException($"Type {type.FullName} is missing a public constructor with one argument of type, or implementing, IPropertySet.");
                 }
 
-                PublishedModelAttribute attribute = type.GetCustomAttribute<PublishedModelAttribute>(false);
+                PublishedModelAttribute? attribute = type.GetCustomAttribute<PublishedModelAttribute>(false);
                 var typeName = attribute == null ? type.Name : attribute.ContentTypeAlias;
 
                 if (modelInfos.TryGetValue(typeName, out var modelInfo))
                 {
-                    throw new InvalidOperationException($"Both types {type.FullName} and {modelInfo.ModelType.FullName} want to be a model type for content type with alias \"{typeName}\".");
+                    throw new InvalidOperationException($"Both types {type.FullName} and {modelInfo.ModelType?.FullName} want to be a model type for content type with alias \"{typeName}\".");
                 }
 
                 // TODO: use Core's ReflectionUtilities.EmitCtor !!
@@ -800,8 +811,12 @@ namespace Umbraco.Cms.Web.Common.ModelsBuilder
             {
                 if (disposing)
                 {
-                    _watcher.EnableRaisingEvents = false;
-                    _watcher.Dispose();
+                    if (_watcher is not null)
+                    {
+                        _watcher.EnableRaisingEvents = false;
+                        _watcher.Dispose();
+                    }
+
                     _locker.Dispose();
                 }
 
@@ -817,20 +832,20 @@ namespace Umbraco.Cms.Web.Common.ModelsBuilder
 
         internal class Infos
         {
-            public Dictionary<string, Type> ModelTypeMap { get; set; }
+            public Dictionary<string, Type>? ModelTypeMap { get; set; }
 
-            public Dictionary<string, ModelInfo> ModelInfos { get; set; }
+            public Dictionary<string, ModelInfo>? ModelInfos { get; set; }
         }
 
         internal class ModelInfo
         {
-            public Type ParameterType { get; set; }
+            public Type? ParameterType { get; set; }
 
-            public Func<IPublishedElement, IPublishedValueFallback, IPublishedElement> Ctor { get; set; }
+            public Func<IPublishedElement, IPublishedValueFallback, IPublishedElement>? Ctor { get; set; }
 
-            public Type ModelType { get; set; }
+            public Type? ModelType { get; set; }
 
-            public Func<IList> ListCtor { get; set; }
+            public Func<IList>? ListCtor { get; set; }
         }
     }
 }
diff --git a/src/Umbraco.Web.Common/ModelsBuilder/ModelsBuilderNotificationHandler.cs b/src/Umbraco.Web.Common/ModelsBuilder/ModelsBuilderNotificationHandler.cs
index ea8408b212..10ee133684 100644
--- a/src/Umbraco.Web.Common/ModelsBuilder/ModelsBuilderNotificationHandler.cs
+++ b/src/Umbraco.Web.Common/ModelsBuilder/ModelsBuilderNotificationHandler.cs
@@ -141,8 +141,8 @@ namespace Umbraco.Cms.Web.Common.ModelsBuilder
         /// </summary>
         public void Handle(ModelBindingErrorNotification notification)
         {
-            ModelsBuilderAssemblyAttribute sourceAttr = notification.SourceType.Assembly.GetCustomAttribute<ModelsBuilderAssemblyAttribute>();
-            ModelsBuilderAssemblyAttribute modelAttr = notification.ModelType.Assembly.GetCustomAttribute<ModelsBuilderAssemblyAttribute>();
+            ModelsBuilderAssemblyAttribute? sourceAttr = notification.SourceType.Assembly.GetCustomAttribute<ModelsBuilderAssemblyAttribute>();
+            ModelsBuilderAssemblyAttribute? modelAttr = notification.ModelType.Assembly.GetCustomAttribute<ModelsBuilderAssemblyAttribute>();
 
             // if source or model is not a ModelsBuider type...
             if (sourceAttr == null || modelAttr == null)
@@ -180,8 +180,8 @@ namespace Umbraco.Cms.Web.Common.ModelsBuilder
                 {
                     // both are pure - report, and if different versions, restart
                     // if same version... makes no sense... and better not restart (loops?)
-                    Version sourceVersion = notification.SourceType.Assembly.GetName().Version;
-                    Version modelVersion = notification.ModelType.Assembly.GetName().Version;
+                    Version? sourceVersion = notification.SourceType.Assembly.GetName().Version;
+                    Version? modelVersion = notification.ModelType.Assembly.GetName().Version;
                     notification.Message.Append(" Both view and content models are in memory generated, with ");
                     notification.Message.Append(sourceVersion == modelVersion
                         ? "same version. The application is in an unstable state and should be restarted."
diff --git a/src/Umbraco.Web.Common/ModelsBuilder/RefreshingRazorViewEngine.cs b/src/Umbraco.Web.Common/ModelsBuilder/RefreshingRazorViewEngine.cs
index 46dba59aba..aafdfa4bb5 100644
--- a/src/Umbraco.Web.Common/ModelsBuilder/RefreshingRazorViewEngine.cs
+++ b/src/Umbraco.Web.Common/ModelsBuilder/RefreshingRazorViewEngine.cs
@@ -95,7 +95,7 @@ namespace Umbraco.Cms.Web.Common.ModelsBuilder
         /// <summary>
         /// When the models change, re-construct the razor stack
         /// </summary>
-        private void InMemoryModelFactoryModelsChanged(object sender, EventArgs e)
+        private void InMemoryModelFactoryModelsChanged(object? sender, EventArgs e)
         {
             _locker.EnterWriteLock();
             try
@@ -121,7 +121,7 @@ namespace Umbraco.Cms.Web.Common.ModelsBuilder
             }
         }
 
-        public string GetAbsolutePath(string executingFilePath, string pagePath)
+        public string? GetAbsolutePath(string? executingFilePath, string? pagePath)
         {
             _locker.EnterReadLock();
             try
@@ -161,7 +161,7 @@ namespace Umbraco.Cms.Web.Common.ModelsBuilder
             }
         }
 
-        public ViewEngineResult GetView(string executingFilePath, string viewPath, bool isMainPage)
+        public ViewEngineResult GetView(string? executingFilePath, string viewPath, bool isMainPage)
         {
             _locker.EnterReadLock();
             try
diff --git a/src/Umbraco.Web.Common/ModelsBuilder/UmbracoAssemblyLoadContext.cs b/src/Umbraco.Web.Common/ModelsBuilder/UmbracoAssemblyLoadContext.cs
index e374a7292f..75c08e8772 100644
--- a/src/Umbraco.Web.Common/ModelsBuilder/UmbracoAssemblyLoadContext.cs
+++ b/src/Umbraco.Web.Common/ModelsBuilder/UmbracoAssemblyLoadContext.cs
@@ -18,6 +18,6 @@ namespace Umbraco.Cms.Web.Common.ModelsBuilder
         }
 
         // we never load anything directly by assembly name. This method will never be called
-        protected override Assembly Load(AssemblyName assemblyName) => null;
+        protected override Assembly? Load(AssemblyName assemblyName) => null;
     }
 }
diff --git a/src/Umbraco.Web.Common/Mvc/HtmlStringUtilities.cs b/src/Umbraco.Web.Common/Mvc/HtmlStringUtilities.cs
index a744b98e70..2194572e77 100644
--- a/src/Umbraco.Web.Common/Mvc/HtmlStringUtilities.cs
+++ b/src/Umbraco.Web.Common/Mvc/HtmlStringUtilities.cs
@@ -31,7 +31,7 @@ namespace Umbraco.Cms.Web.Common.Mvc
             return new HtmlString(value);
         }
 
-        public HtmlString StripHtmlTags(string html, params string[] tags)
+        public HtmlString StripHtmlTags(string html, params string[]? tags)
         {
             var doc = new HtmlDocument();
             doc.LoadHtml("<p>" + html + "</p>");
@@ -46,7 +46,7 @@ namespace Umbraco.Cms.Web.Common.Mvc
                     //is element
                     if (node.NodeType != HtmlNodeType.Element) continue;
                     var filterAllTags = (tags == null || !tags.Any());
-                    if (filterAllTags || tags.Any(tag => string.Equals(tag, node.Name, StringComparison.CurrentCultureIgnoreCase)))
+                    if (filterAllTags || (tags?.Any(tag => string.Equals(tag, node.Name, StringComparison.CurrentCultureIgnoreCase)) ?? false))
                     {
                         targets.Add(node);
                     }
diff --git a/src/Umbraco.Web.Common/Profiler/InitializeWebProfiling.cs b/src/Umbraco.Web.Common/Profiler/InitializeWebProfiling.cs
index 45901314a6..cdd6d0aee9 100644
--- a/src/Umbraco.Web.Common/Profiler/InitializeWebProfiling.cs
+++ b/src/Umbraco.Web.Common/Profiler/InitializeWebProfiling.cs
@@ -15,7 +15,7 @@ namespace Umbraco.Cms.Web.Common.Profiler
     public class InitializeWebProfiling : INotificationHandler<UmbracoApplicationStartingNotification>
     {
         private readonly bool _profile;
-        private readonly WebProfiler _profiler;
+        private readonly WebProfiler? _profiler;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="InitializeWebProfiling"/> class.
@@ -48,7 +48,7 @@ namespace Umbraco.Cms.Web.Common.Profiler
             if (_profile && notification.RuntimeLevel == RuntimeLevel.Run)
             {
                 // Stop the profiling of the booting process
-                _profiler.StopBoot();
+                _profiler?.StopBoot();
             }
         }
 
diff --git a/src/Umbraco.Web.Common/Profiler/WebProfiler.cs b/src/Umbraco.Web.Common/Profiler/WebProfiler.cs
index 688414b3de..fe1aa710d4 100644
--- a/src/Umbraco.Web.Common/Profiler/WebProfiler.cs
+++ b/src/Umbraco.Web.Common/Profiler/WebProfiler.cs
@@ -24,12 +24,12 @@ namespace Umbraco.Cms.Web.Common.Profiler
         {
             _ = x;
         });
-        private MiniProfiler _startupProfiler;
+        private MiniProfiler? _startupProfiler;
         private int _first;
 
 
 
-        public IDisposable Step(string name)
+        public IDisposable? Step(string name)
         {
             return MiniProfiler.Current?.Step(name);
         }
@@ -42,7 +42,7 @@ namespace Umbraco.Cms.Web.Common.Profiler
 
         public void StartBoot() => _startupProfiler = MiniProfiler.StartNew("Startup Profiler");
 
-        public void StopBoot() => _startupProfiler.Stop();
+        public void StopBoot() => _startupProfiler?.Stop();
 
         public void Stop(bool discardResults = false) => MiniProfilerContext.Value?.Stop(discardResults);
 
@@ -80,7 +80,10 @@ namespace Umbraco.Cms.Web.Common.Profiler
                     var first = Interlocked.Exchange(ref _first, 1) == 0;
                     if (first)
                     {
-                        AddSubProfiler(_startupProfiler);
+                        if (_startupProfiler is not null)
+                        {
+                            AddSubProfiler(_startupProfiler);
+                        }
 
                         _startupProfiler = null;
                     }
@@ -110,10 +113,12 @@ namespace Umbraco.Cms.Web.Common.Profiler
         private void AddSubProfiler(MiniProfiler subProfiler)
         {
             var startupDuration = subProfiler.Root.DurationMilliseconds.GetValueOrDefault();
-            MiniProfilerContext.Value.DurationMilliseconds += startupDuration;
-            MiniProfilerContext.Value.GetTimingHierarchy().First().DurationMilliseconds += startupDuration;
-            MiniProfilerContext.Value.Root.AddChild(subProfiler.Root);
-
+            if (MiniProfilerContext.Value is not null)
+            {
+                MiniProfilerContext.Value.DurationMilliseconds += startupDuration;
+                MiniProfilerContext.Value.GetTimingHierarchy().First().DurationMilliseconds += startupDuration;
+                MiniProfilerContext.Value.Root.AddChild(subProfiler.Root);
+            }
         }
 
         private static bool ShouldProfile(HttpRequest request)
diff --git a/src/Umbraco.Web.Common/Profiler/WebProfilerHtml.cs b/src/Umbraco.Web.Common/Profiler/WebProfilerHtml.cs
index 037e5e40ad..f061c58242 100644
--- a/src/Umbraco.Web.Common/Profiler/WebProfilerHtml.cs
+++ b/src/Umbraco.Web.Common/Profiler/WebProfilerHtml.cs
@@ -34,7 +34,7 @@ namespace Umbraco.Cms.Web.Common.Profiler
 
             var result = StackExchange.Profiling.Internal.Render.Includes(
                 profiler,
-                path: context.Request.PathBase + path,
+                path: context is not null ? context.Request.PathBase + path : null,
                 isAuthorized: true,
                 requestIDs: new List<Guid> { profiler.Id },
                 position: RenderPosition.Right,
diff --git a/src/Umbraco.Web.Common/Routing/RoutableDocumentFilter.cs b/src/Umbraco.Web.Common/Routing/RoutableDocumentFilter.cs
index 125a11ef1c..355c73c663 100644
--- a/src/Umbraco.Web.Common/Routing/RoutableDocumentFilter.cs
+++ b/src/Umbraco.Web.Common/Routing/RoutableDocumentFilter.cs
@@ -29,7 +29,7 @@ namespace Umbraco.Cms.Web.Common.Routing
         private readonly object _routeLocker = new object();
         private object _initLocker = new object();
         private bool _isInit = false;
-        private HashSet<string> _reservedList;
+        private HashSet<string>? _reservedList;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="RoutableDocumentFilter"/> class.
@@ -134,7 +134,7 @@ namespace Umbraco.Cms.Web.Common.Routing
             }
 
             // return true if URL starts with an element of the reserved list
-            var isReserved = _reservedList.Any(x => absPath.InvariantStartsWith(x));
+            var isReserved = _reservedList?.Any(x => absPath.InvariantStartsWith(x)) ?? false;
 
             if (isReserved)
             {
@@ -170,7 +170,7 @@ namespace Umbraco.Cms.Web.Common.Routing
             // Borrowed and modified from https://stackoverflow.com/a/59550580
 
             // Return a collection of Microsoft.AspNetCore.Http.Endpoint instances.
-            IEnumerable<RouteEndpoint> routeEndpoints = _endpointDataSource?.Endpoints
+            IEnumerable<RouteEndpoint>? routeEndpoints = _endpointDataSource?.Endpoints
                 .OfType<RouteEndpoint>()
                 .Where(x =>
                 {
@@ -195,10 +195,10 @@ namespace Umbraco.Cms.Web.Common.Routing
             var routeValues = new RouteValueDictionary();
 
             // To get the matchedEndpoint of the provide url
-            RouteEndpoint matchedEndpoint = routeEndpoints?
+            RouteEndpoint? matchedEndpoint = routeEndpoints?
                 .Where(e => e.RoutePattern.RawText != null)
                 .Where(e => new TemplateMatcher(
-                        TemplateParser.Parse(e.RoutePattern.RawText),
+                        TemplateParser.Parse(e.RoutePattern.RawText!),
                         new RouteValueDictionary())
                     .TryMatch(absPath, routeValues))
                 .OrderBy(c => c.Order)
diff --git a/src/Umbraco.Web.Common/Routing/UmbracoRouteValues.cs b/src/Umbraco.Web.Common/Routing/UmbracoRouteValues.cs
index 6088f21931..d06f9bcd28 100644
--- a/src/Umbraco.Web.Common/Routing/UmbracoRouteValues.cs
+++ b/src/Umbraco.Web.Common/Routing/UmbracoRouteValues.cs
@@ -21,7 +21,7 @@ namespace Umbraco.Cms.Web.Common.Routing
         public UmbracoRouteValues(
             IPublishedRequest publishedRequest,
             ControllerActionDescriptor controllerActionDescriptor,
-            string templateName = null)
+            string? templateName = null)
         {
             PublishedRequest = publishedRequest;
             ControllerActionDescriptor = controllerActionDescriptor;
@@ -41,7 +41,7 @@ namespace Umbraco.Cms.Web.Common.Routing
         /// <summary>
         /// Gets the template name
         /// </summary>
-        public string TemplateName { get; }
+        public string? TemplateName { get; }
 
         /// <summary>
         /// Gets the controller type
diff --git a/src/Umbraco.Web.Common/RuntimeMinification/SmidgeHelperAccessor.cs b/src/Umbraco.Web.Common/RuntimeMinification/SmidgeHelperAccessor.cs
index 198fe7a5d0..b1dc202a37 100644
--- a/src/Umbraco.Web.Common/RuntimeMinification/SmidgeHelperAccessor.cs
+++ b/src/Umbraco.Web.Common/RuntimeMinification/SmidgeHelperAccessor.cs
@@ -22,7 +22,7 @@ namespace Umbraco.Cms.Web.Common.RuntimeMinification
                 var httpContext = _httpContextAccessor.HttpContext;
                 if (httpContext == null)
                     throw new InvalidOperationException($"Cannot get a {nameof(SmidgeHelper)} instance since there is no current http request");
-                return httpContext.RequestServices.GetService<SmidgeHelper>();
+                return httpContext.RequestServices.GetService<SmidgeHelper>()!;
             }
         }
     }
diff --git a/src/Umbraco.Web.Common/RuntimeMinification/SmidgeRuntimeMinifier.cs b/src/Umbraco.Web.Common/RuntimeMinification/SmidgeRuntimeMinifier.cs
index 6e24c06b8e..992c676618 100644
--- a/src/Umbraco.Web.Common/RuntimeMinification/SmidgeRuntimeMinifier.cs
+++ b/src/Umbraco.Web.Common/RuntimeMinification/SmidgeRuntimeMinifier.cs
@@ -36,7 +36,7 @@ namespace Umbraco.Cms.Web.Common.RuntimeMinification
         private readonly Lazy<PreProcessPipeline> _jsNonOptimizedPipeline;
         private readonly Lazy<PreProcessPipeline> _cssOptimizedPipeline;
         private readonly Lazy<PreProcessPipeline> _cssNonOptimizedPipeline;
-        private ICacheBuster _cacheBuster;
+        private ICacheBuster? _cacheBuster;
         private readonly Type _cacheBusterType;
 
         public SmidgeRuntimeMinifier(
@@ -88,9 +88,9 @@ namespace Umbraco.Cms.Web.Common.RuntimeMinification
         public string CacheBuster => (_cacheBuster ??= _cacheBusterResolver.GetCacheBuster(_cacheBusterType)).GetValue();
 
         // only issue with creating bundles like this is that we don't have full control over the bundle options, though that could
-        public void CreateCssBundle(string bundleName, BundlingOptions bundleOptions, params string[] filePaths)
+        public void CreateCssBundle(string bundleName, BundlingOptions bundleOptions, params string[]? filePaths)
         {
-            if (filePaths.Any(f => !f.StartsWith("/") && !f.StartsWith("~/")))
+            if (filePaths?.Any(f => !f.StartsWith("/") && !f.StartsWith("~/")) ?? false)
             {
                 throw new InvalidOperationException("All file paths must be absolute");
             }
@@ -110,9 +110,9 @@ namespace Umbraco.Cms.Web.Common.RuntimeMinification
 
         public async Task<string> RenderCssHereAsync(string bundleName) => (await _smidge.SmidgeHelper.CssHereAsync(bundleName, _hostingEnvironment.IsDebugMode)).ToString();
 
-        public void CreateJsBundle(string bundleName, BundlingOptions bundleOptions, params string[] filePaths)
+        public void CreateJsBundle(string bundleName, BundlingOptions bundleOptions, params string[]? filePaths)
         {
-            if (filePaths.Any(f => !f.StartsWith("/") && !f.StartsWith("~/")))
+            if (filePaths?.Any(f => !f.StartsWith("/") && !f.StartsWith("~/")) ?? false)
             {
                 throw new InvalidOperationException("All file paths must be absolute");
             }
diff --git a/src/Umbraco.Web.Common/RuntimeMinification/UmbracoSmidgeConfigCacheBuster.cs b/src/Umbraco.Web.Common/RuntimeMinification/UmbracoSmidgeConfigCacheBuster.cs
index c323204148..b3d114e103 100644
--- a/src/Umbraco.Web.Common/RuntimeMinification/UmbracoSmidgeConfigCacheBuster.cs
+++ b/src/Umbraco.Web.Common/RuntimeMinification/UmbracoSmidgeConfigCacheBuster.cs
@@ -39,7 +39,7 @@ namespace Umbraco.Cms.Web.Common.RuntimeMinification
         private readonly IUmbracoVersion _umbracoVersion;
         private readonly IEntryAssemblyMetadata _entryAssemblyMetadata;
 
-        private string _cacheBusterValue;
+        private string? _cacheBusterValue;
 
         public UmbracoSmidgeConfigCacheBuster(
             IOptions<RuntimeMinificationSettings> runtimeMinificationSettings,
diff --git a/src/Umbraco.Web.Common/Security/BackOfficeSecurityAccessor.cs b/src/Umbraco.Web.Common/Security/BackOfficeSecurityAccessor.cs
index d98877e1c7..bcb74aa286 100644
--- a/src/Umbraco.Web.Common/Security/BackOfficeSecurityAccessor.cs
+++ b/src/Umbraco.Web.Common/Security/BackOfficeSecurityAccessor.cs
@@ -16,7 +16,7 @@ namespace Umbraco.Cms.Web.Common.Security
         /// <summary>
         /// Gets the current <see cref="IBackOfficeSecurity"/> object.
         /// </summary>
-        public IBackOfficeSecurity BackOfficeSecurity
+        public IBackOfficeSecurity? BackOfficeSecurity
             => _httpContextAccessor.HttpContext?.RequestServices?.GetService<IBackOfficeSecurity>();
     }
 }
diff --git a/src/Umbraco.Web.Common/Security/BackOfficeUserManager.cs b/src/Umbraco.Web.Common/Security/BackOfficeUserManager.cs
index 505abdbe0e..aa3323e101 100644
--- a/src/Umbraco.Web.Common/Security/BackOfficeUserManager.cs
+++ b/src/Umbraco.Web.Common/Security/BackOfficeUserManager.cs
@@ -169,18 +169,18 @@ namespace Umbraco.Cms.Web.Common.Security
             return result;
         }
 
-        private string GetCurrentUserId(IPrincipal currentUser)
+        private string GetCurrentUserId(IPrincipal? currentUser)
         {
-            ClaimsIdentity umbIdentity = currentUser?.GetUmbracoIdentity();
+            ClaimsIdentity? umbIdentity = currentUser?.GetUmbracoIdentity();
             var currentUserId = umbIdentity?.GetUserId<string>() ?? Core.Constants.Security.SuperUserIdAsString;
             return currentUserId;
         }
 
-        public void NotifyAccountLocked(IPrincipal currentUser, string userId) => Notify(currentUser,
+        public void NotifyAccountLocked(IPrincipal? currentUser, string userId) => Notify(currentUser,
             (currentUserId, ip) => new UserLockedNotification(ip, userId, currentUserId)
         );
 
-        public void NotifyAccountUnlocked(IPrincipal currentUser, string userId) => Notify(currentUser,
+        public void NotifyAccountUnlocked(IPrincipal? currentUser, string userId) => Notify(currentUser,
             (currentUserId, ip) => new UserUnlockedNotification(ip, userId, currentUserId)
         );
 
@@ -192,7 +192,7 @@ namespace Umbraco.Cms.Web.Common.Security
             (currentUserId, ip) => new UserForgotPasswordChangedNotification(ip, userId, currentUserId)
         );
 
-        public void NotifyLoginFailed(IPrincipal currentUser, string userId) => Notify(currentUser,
+        public void NotifyLoginFailed(IPrincipal? currentUser, string userId) => Notify(currentUser,
             (currentUserId, ip) => new UserLoginFailedNotification(ip, userId, currentUserId)
         );
 
@@ -213,19 +213,19 @@ namespace Umbraco.Cms.Web.Common.Security
             return new SignOutSuccessResult { SignOutRedirectUrl = notification.SignOutRedirectUrl };
         }
 
-        public void NotifyPasswordChanged(IPrincipal currentUser, string userId) => Notify(currentUser,
+        public void NotifyPasswordChanged(IPrincipal? currentUser, string userId) => Notify(currentUser,
             (currentUserId, ip) => new UserPasswordChangedNotification(ip, userId, currentUserId)
         );
 
-        public void NotifyPasswordReset(IPrincipal currentUser, string userId) => Notify(currentUser,
+        public void NotifyPasswordReset(IPrincipal? currentUser, string userId) => Notify(currentUser,
             (currentUserId, ip) => new UserPasswordResetNotification(ip, userId, currentUserId)
         );
 
-        public void NotifyResetAccessFailedCount(IPrincipal currentUser, string userId) => Notify(currentUser,
+        public void NotifyResetAccessFailedCount(IPrincipal? currentUser, string userId) => Notify(currentUser,
             (currentUserId, ip) => new UserResetAccessFailedCountNotification(ip, userId, currentUserId)
         );
 
-        private T Notify<T>(IPrincipal currentUser, Func<string, string, T> createNotification) where T : INotification
+        private T Notify<T>(IPrincipal? currentUser, Func<string, string, T> createNotification) where T : INotification
         {
             var currentUserId = GetCurrentUserId(currentUser);
             var ip = IpResolver.GetCurrentRequestIpAddress();
diff --git a/src/Umbraco.Web.Common/Security/BackofficeSecurity.cs b/src/Umbraco.Web.Common/Security/BackofficeSecurity.cs
index 13ff104265..8630197650 100644
--- a/src/Umbraco.Web.Common/Security/BackofficeSecurity.cs
+++ b/src/Umbraco.Web.Common/Security/BackofficeSecurity.cs
@@ -14,7 +14,7 @@ namespace Umbraco.Cms.Web.Common.Security
         private readonly IHttpContextAccessor _httpContextAccessor;
 
         private readonly object _currentUserLock = new object();
-        private IUser _currentUser;
+        private IUser? _currentUser;
 
         public BackOfficeSecurity(
             IUserService userService,
@@ -25,7 +25,7 @@ namespace Umbraco.Cms.Web.Common.Security
         }
 
         /// <inheritdoc />
-        public IUser CurrentUser
+        public IUser? CurrentUser
         {
             get
             {
@@ -55,15 +55,15 @@ namespace Umbraco.Cms.Web.Common.Security
         /// <inheritdoc />
         public Attempt<int?> GetUserId()
         {
-            ClaimsIdentity identity = _httpContextAccessor.HttpContext?.GetCurrentIdentity();
+            ClaimsIdentity? identity = _httpContextAccessor.HttpContext?.GetCurrentIdentity();
             return identity == null ? Attempt.Fail<int?>() : Attempt.Succeed(identity.GetId());
         }
 
         /// <inheritdoc />
         public bool IsAuthenticated()
         {
-            HttpContext httpContext = _httpContextAccessor.HttpContext;
-            return httpContext?.User != null && httpContext.User.Identity.IsAuthenticated && httpContext.GetCurrentIdentity() != null;
+            HttpContext? httpContext = _httpContextAccessor.HttpContext;
+            return httpContext?.User != null && (httpContext.User.Identity?.IsAuthenticated ?? false) && httpContext.GetCurrentIdentity() != null;
         }
 
         /// <inheritdoc />
diff --git a/src/Umbraco.Web.Common/Security/EncryptionHelper.cs b/src/Umbraco.Web.Common/Security/EncryptionHelper.cs
index 48154d7c8f..8c9ebe2fff 100644
--- a/src/Umbraco.Web.Common/Security/EncryptionHelper.cs
+++ b/src/Umbraco.Web.Common/Security/EncryptionHelper.cs
@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Collections.Specialized;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Net;
 using System.Web;
@@ -30,7 +31,7 @@ namespace Umbraco.Cms.Web.Common.Security
         /// This is used in methods like BeginUmbracoForm and SurfaceAction to generate an encrypted string which gets submitted in a request for which
         /// Umbraco can decrypt during the routing process in order to delegate the request to a specific MVC Controller.
         /// </summary>
-        public static string CreateEncryptedRouteString(IDataProtectionProvider dataProtectionProvider, string controllerName, string controllerAction, string area, object additionalRouteVals = null)
+        public static string CreateEncryptedRouteString(IDataProtectionProvider dataProtectionProvider, string controllerName, string controllerAction, string area, object? additionalRouteVals = null)
         {
             if (dataProtectionProvider is null)
             {
@@ -56,7 +57,7 @@ namespace Umbraco.Cms.Web.Common.Security
             var surfaceRouteParams = $"{ViewConstants.ReservedAdditionalKeys.Controller}={WebUtility.UrlEncode(controllerName)}&{ViewConstants.ReservedAdditionalKeys.Action}={WebUtility.UrlEncode(controllerAction)}&{ViewConstants.ReservedAdditionalKeys.Area}={area}";
 
             // checking if the additional route values is already a dictionary and convert to querystring
-            string additionalRouteValsAsQuery;
+            string? additionalRouteValsAsQuery;
             if (additionalRouteVals != null)
             {
                 if (additionalRouteVals is Dictionary<string, object> additionalRouteValsAsDictionary)
@@ -81,7 +82,7 @@ namespace Umbraco.Cms.Web.Common.Security
             return Encrypt(surfaceRouteParams, dataProtectionProvider);
         }
 
-        public static bool DecryptAndValidateEncryptedRouteString(IDataProtectionProvider dataProtectionProvider, string encryptedString, out IDictionary<string, string> parts)
+        public static bool DecryptAndValidateEncryptedRouteString(IDataProtectionProvider dataProtectionProvider, string encryptedString, [MaybeNullWhen(false)] out IDictionary<string, string?> parts)
         {
             if (dataProtectionProvider == null)
             {
@@ -101,10 +102,13 @@ namespace Umbraco.Cms.Web.Common.Security
             }
 
             NameValueCollection parsedQueryString = HttpUtility.ParseQueryString(decryptedString);
-            parts = new Dictionary<string, string>();
+            parts = new Dictionary<string, string?>();
             foreach (var key in parsedQueryString.AllKeys)
             {
-                parts[key] = parsedQueryString[key];
+                if (key is not null)
+                {
+                    parts[key] = parsedQueryString[key];
+                }
             }
 
             // validate all required keys exist
diff --git a/src/Umbraco.Web.Common/Security/IBackOfficeSignInManager.cs b/src/Umbraco.Web.Common/Security/IBackOfficeSignInManager.cs
index 38ed6ba74a..0c7ff39c02 100644
--- a/src/Umbraco.Web.Common/Security/IBackOfficeSignInManager.cs
+++ b/src/Umbraco.Web.Common/Security/IBackOfficeSignInManager.cs
@@ -12,14 +12,14 @@ namespace Umbraco.Cms.Web.BackOffice.Security
     /// </summary>
     public interface IBackOfficeSignInManager
     {
-        AuthenticationProperties ConfigureExternalAuthenticationProperties(string provider, string redirectUrl, string userId = null);
+        AuthenticationProperties ConfigureExternalAuthenticationProperties(string provider, string redirectUrl, string? userId = null);
         Task<SignInResult> ExternalLoginSignInAsync(ExternalLoginInfo loginInfo, bool isPersistent, bool bypassTwoFactor = false);
         Task<IEnumerable<AuthenticationScheme>> GetExternalAuthenticationSchemesAsync();
-        Task<ExternalLoginInfo> GetExternalLoginInfoAsync(string expectedXsrf = null);
+        Task<ExternalLoginInfo> GetExternalLoginInfoAsync(string? expectedXsrf = null);
         Task<BackOfficeIdentityUser> GetTwoFactorAuthenticationUserAsync();
         Task<SignInResult> PasswordSignInAsync(string userName, string password, bool isPersistent, bool lockoutOnFailure);
         Task SignOutAsync();
-        Task SignInAsync(BackOfficeIdentityUser user, bool isPersistent, string authenticationMethod = null);
+        Task SignInAsync(BackOfficeIdentityUser user, bool isPersistent, string? authenticationMethod = null);
         Task<ClaimsPrincipal> CreateUserPrincipalAsync(BackOfficeIdentityUser user);
         Task<SignInResult> TwoFactorSignInAsync(string provider, string code, bool isPersistent, bool rememberClient);
         Task<IdentityResult> UpdateExternalAuthenticationTokensAsync(ExternalLoginInfo externalLogin);
diff --git a/src/Umbraco.Web.Common/Security/IMemberExternalLoginProviders.cs b/src/Umbraco.Web.Common/Security/IMemberExternalLoginProviders.cs
index b3d6813c2f..50beb1f65a 100644
--- a/src/Umbraco.Web.Common/Security/IMemberExternalLoginProviders.cs
+++ b/src/Umbraco.Web.Common/Security/IMemberExternalLoginProviders.cs
@@ -14,7 +14,7 @@ namespace Umbraco.Cms.Web.Common.Security
         /// </summary>
         /// <param name="authenticationType"></param>
         /// <returns></returns>
-        Task<MemberExternalLoginProviderScheme> GetAsync(string authenticationType);
+        Task<MemberExternalLoginProviderScheme?> GetAsync(string authenticationType);
 
         /// <summary>
         /// Get all registered <see cref="BackOfficeExternalLoginProvider"/>
diff --git a/src/Umbraco.Web.Common/Security/IMemberSignInManager.cs b/src/Umbraco.Web.Common/Security/IMemberSignInManager.cs
index 4ba5caca9b..04d591866d 100644
--- a/src/Umbraco.Web.Common/Security/IMemberSignInManager.cs
+++ b/src/Umbraco.Web.Common/Security/IMemberSignInManager.cs
@@ -9,7 +9,7 @@ namespace Umbraco.Cms.Web.Common.Security
     {
         // TODO: We could have a base interface for these to share with IBackOfficeSignInManager
         Task<SignInResult> PasswordSignInAsync(string userName, string password, bool isPersistent, bool lockoutOnFailure);
-        Task SignInAsync(MemberIdentityUser user, bool isPersistent, string authenticationMethod = null);
+        Task SignInAsync(MemberIdentityUser user, bool isPersistent, string? authenticationMethod = null);
         Task SignOutAsync();
     }
 }
diff --git a/src/Umbraco.Web.Common/Security/IMemberSignInManagerExternalLogins.cs b/src/Umbraco.Web.Common/Security/IMemberSignInManagerExternalLogins.cs
index eb6a66a000..20fe99b30a 100644
--- a/src/Umbraco.Web.Common/Security/IMemberSignInManagerExternalLogins.cs
+++ b/src/Umbraco.Web.Common/Security/IMemberSignInManagerExternalLogins.cs
@@ -9,8 +9,8 @@ namespace Umbraco.Cms.Web.Common.Security
     [Obsolete("This interface will be merged with IMemberSignInManager in Umbraco 10")]
     public interface IMemberSignInManagerExternalLogins : IMemberSignInManager
     {
-        AuthenticationProperties ConfigureExternalAuthenticationProperties(string provider, string redirectUrl, string userId = null);
-        Task<ExternalLoginInfo> GetExternalLoginInfoAsync(string expectedXsrf = null);
+        AuthenticationProperties ConfigureExternalAuthenticationProperties(string provider, string redirectUrl, string? userId = null);
+        Task<ExternalLoginInfo?> GetExternalLoginInfoAsync(string? expectedXsrf = null);
         Task<IdentityResult> UpdateExternalAuthenticationTokensAsync(ExternalLoginInfo externalLogin);
         Task<SignInResult> ExternalLoginSignInAsync(ExternalLoginInfo loginInfo, bool isPersistent, bool bypassTwoFactor = false);
         Task<MemberIdentityUser> GetTwoFactorAuthenticationUserAsync();
diff --git a/src/Umbraco.Web.Common/Security/MemberCookieManager.cs b/src/Umbraco.Web.Common/Security/MemberCookieManager.cs
index 9e176d15c1..bdc4306e55 100644
--- a/src/Umbraco.Web.Common/Security/MemberCookieManager.cs
+++ b/src/Umbraco.Web.Common/Security/MemberCookieManager.cs
@@ -54,7 +54,7 @@ namespace Umbraco.Cms.Web.Common.Security
         /// Explicitly implement this so that we filter the request
         /// </summary>
         /// <inheritdoc/>
-        string ICookieManager.GetRequestCookie(HttpContext context, string key)
+        string? ICookieManager.GetRequestCookie(HttpContext context, string key)
         {
             var absPath = context.Request.Path;
 
diff --git a/src/Umbraco.Web.Common/Security/MemberExternalLoginProvider.cs b/src/Umbraco.Web.Common/Security/MemberExternalLoginProvider.cs
index 9681d47413..e146f7bc2c 100644
--- a/src/Umbraco.Web.Common/Security/MemberExternalLoginProvider.cs
+++ b/src/Umbraco.Web.Common/Security/MemberExternalLoginProvider.cs
@@ -28,8 +28,8 @@ namespace Umbraco.Cms.Web.Common.Security
 
         public MemberExternalLoginProviderOptions Options { get; }
 
-        public override bool Equals(object obj) => Equals(obj as MemberExternalLoginProvider);
-        public bool Equals(MemberExternalLoginProvider other) => other != null && AuthenticationType == other.AuthenticationType;
+        public override bool Equals(object? obj) => Equals(obj as MemberExternalLoginProvider);
+        public bool Equals(MemberExternalLoginProvider? other) => other != null && AuthenticationType == other.AuthenticationType;
         public override int GetHashCode() => HashCode.Combine(AuthenticationType);
     }
 
diff --git a/src/Umbraco.Web.Common/Security/MemberExternalLoginProviderOptions.cs b/src/Umbraco.Web.Common/Security/MemberExternalLoginProviderOptions.cs
index ea93a522da..3a98b701d7 100644
--- a/src/Umbraco.Web.Common/Security/MemberExternalLoginProviderOptions.cs
+++ b/src/Umbraco.Web.Common/Security/MemberExternalLoginProviderOptions.cs
@@ -6,9 +6,9 @@ namespace Umbraco.Cms.Web.Common.Security
     public class MemberExternalLoginProviderOptions
     {
         public MemberExternalLoginProviderOptions(
-            MemberExternalSignInAutoLinkOptions autoLinkOptions = null,
+            MemberExternalSignInAutoLinkOptions? autoLinkOptions = null,
             bool autoRedirectLoginToExternalProvider = false,
-            string customBackOfficeView = null)
+            string? customBackOfficeView = null)
         {
             AutoLinkOptions = autoLinkOptions ?? new MemberExternalSignInAutoLinkOptions();
         }
diff --git a/src/Umbraco.Web.Common/Security/MemberExternalLoginProviderScheme.cs b/src/Umbraco.Web.Common/Security/MemberExternalLoginProviderScheme.cs
index 600405b638..423fa899e4 100644
--- a/src/Umbraco.Web.Common/Security/MemberExternalLoginProviderScheme.cs
+++ b/src/Umbraco.Web.Common/Security/MemberExternalLoginProviderScheme.cs
@@ -7,7 +7,7 @@ namespace Umbraco.Cms.Web.Common.Security
     {
         public MemberExternalLoginProviderScheme(
             MemberExternalLoginProvider externalLoginProvider,
-            AuthenticationScheme authenticationScheme)
+            AuthenticationScheme? authenticationScheme)
         {
             ExternalLoginProvider = externalLoginProvider ?? throw new ArgumentNullException(nameof(externalLoginProvider));
             AuthenticationScheme = authenticationScheme ?? throw new ArgumentNullException(nameof(authenticationScheme));
diff --git a/src/Umbraco.Web.Common/Security/MemberExternalLoginProviders.cs b/src/Umbraco.Web.Common/Security/MemberExternalLoginProviders.cs
index 28102c434f..41b298d903 100644
--- a/src/Umbraco.Web.Common/Security/MemberExternalLoginProviders.cs
+++ b/src/Umbraco.Web.Common/Security/MemberExternalLoginProviders.cs
@@ -23,18 +23,18 @@ namespace Umbraco.Cms.Web.Common.Security
         }
 
         /// <inheritdoc />
-        public async Task<MemberExternalLoginProviderScheme> GetAsync(string authenticationType)
+        public async Task<MemberExternalLoginProviderScheme?> GetAsync(string authenticationType)
         {
             var schemaName =
                 authenticationType.EnsureStartsWith(Core.Constants.Security.MemberExternalAuthenticationTypePrefix);
 
-            if (!_externalLogins.TryGetValue(schemaName, out MemberExternalLoginProvider provider))
+            if (!_externalLogins.TryGetValue(schemaName, out MemberExternalLoginProvider? provider))
             {
                 return null;
             }
 
             // get the associated scheme
-            AuthenticationScheme associatedScheme = await _authenticationSchemeProvider.GetSchemeAsync(provider.AuthenticationType);
+            AuthenticationScheme? associatedScheme = await _authenticationSchemeProvider.GetSchemeAsync(provider.AuthenticationType);
 
             if (associatedScheme == null)
             {
@@ -51,7 +51,7 @@ namespace Umbraco.Cms.Web.Common.Security
             foreach (MemberExternalLoginProvider login in _externalLogins.Values)
             {
                 // get the associated scheme
-                AuthenticationScheme associatedScheme = await _authenticationSchemeProvider.GetSchemeAsync(login.AuthenticationType);
+                AuthenticationScheme? associatedScheme = await _authenticationSchemeProvider.GetSchemeAsync(login.AuthenticationType);
 
                 providersWithSchemes.Add(new MemberExternalLoginProviderScheme(login, associatedScheme));
             }
diff --git a/src/Umbraco.Web.Common/Security/MemberExternalSignInAutoLinkOptions.cs b/src/Umbraco.Web.Common/Security/MemberExternalSignInAutoLinkOptions.cs
index 42dcf6d56f..21ce550196 100644
--- a/src/Umbraco.Web.Common/Security/MemberExternalSignInAutoLinkOptions.cs
+++ b/src/Umbraco.Web.Common/Security/MemberExternalSignInAutoLinkOptions.cs
@@ -13,7 +13,7 @@ namespace Umbraco.Cms.Web.Common.Security
     /// </summary>
     public class MemberExternalSignInAutoLinkOptions
     {
-        private readonly string _defaultCulture;
+        private readonly string? _defaultCulture;
 
         /// <summary>
         ///     Initializes a new instance of the <see cref="MemberExternalSignInAutoLinkOptions" /> class.
@@ -22,8 +22,8 @@ namespace Umbraco.Cms.Web.Common.Security
             bool autoLinkExternalAccount = false,
             bool defaultIsApproved = true,
             string defaultMemberTypeAlias = Core.Constants.Conventions.MemberTypes.DefaultAlias,
-            string defaultCulture = null,
-            IEnumerable<string> defaultMemberGroups = null)
+            string? defaultCulture = null,
+            IEnumerable<string>? defaultMemberGroups = null)
         {
             AutoLinkExternalAccount = autoLinkExternalAccount;
             DefaultIsApproved = defaultIsApproved;
@@ -36,14 +36,14 @@ namespace Umbraco.Cms.Web.Common.Security
         ///     A callback executed during account auto-linking and before the user is persisted
         /// </summary>
         [IgnoreDataMember]
-        public Action<MemberIdentityUser, ExternalLoginInfo> OnAutoLinking { get; set; }
+        public Action<MemberIdentityUser, ExternalLoginInfo>? OnAutoLinking { get; set; }
 
         /// <summary>
         ///     A callback executed during every time a user authenticates using an external login.
         ///     returns a boolean indicating if sign in should continue or not.
         /// </summary>
         [IgnoreDataMember]
-        public Func<MemberIdentityUser, ExternalLoginInfo, bool> OnExternalLogin { get; set; }
+        public Func<MemberIdentityUser, ExternalLoginInfo, bool>? OnExternalLogin { get; set; }
 
         /// <summary>
         ///     Gets a value indicating whether flag indicating if logging in with the external provider should auto-link/create a
diff --git a/src/Umbraco.Web.Common/Security/MemberManager.cs b/src/Umbraco.Web.Common/Security/MemberManager.cs
index dad9fddad2..f9f4f3d0bb 100644
--- a/src/Umbraco.Web.Common/Security/MemberManager.cs
+++ b/src/Umbraco.Web.Common/Security/MemberManager.cs
@@ -22,7 +22,7 @@ namespace Umbraco.Cms.Web.Common.Security
         private readonly IMemberUserStore _store;
         private readonly IPublicAccessService _publicAccessService;
         private readonly IHttpContextAccessor _httpContextAccessor;
-        private MemberIdentityUser _currentMember;
+        private MemberIdentityUser? _currentMember;
 
         public MemberManager(
             IIpResolver ipResolver,
@@ -49,7 +49,7 @@ namespace Umbraco.Cms.Web.Common.Security
         public override bool SupportsUserTwoFactor => true;
 
         /// <inheritdoc />
-        public async Task<bool> IsMemberAuthorizedAsync(IEnumerable<string> allowTypes = null, IEnumerable<string> allowGroups = null, IEnumerable<int> allowMembers = null)
+        public async Task<bool> IsMemberAuthorizedAsync(IEnumerable<string>? allowTypes = null, IEnumerable<string>? allowGroups = null, IEnumerable<int>? allowMembers = null)
         {
             if (allowTypes == null)
             {
@@ -76,7 +76,7 @@ namespace Umbraco.Cms.Web.Common.Security
             }
             else
             {
-                MemberIdentityUser currentMember = await GetCurrentMemberAsync();
+                MemberIdentityUser? currentMember = await GetCurrentMemberAsync();
 
                 // If a member could not be resolved from the provider, we are clearly not authorized and can break right here
                 if (currentMember == null)
@@ -91,7 +91,7 @@ namespace Umbraco.Cms.Web.Common.Security
                 if (allowTypesList.Any(allowType => allowType != string.Empty))
                 {
                     // Allow only if member's type is in list
-                    allowAction = allowTypesList.Select(x => x.ToLowerInvariant()).Contains(currentMember.MemberTypeAlias.ToLowerInvariant());
+                    allowAction = allowTypesList.Select(x => x.ToLowerInvariant()).Contains(currentMember.MemberTypeAlias?.ToLowerInvariant());
                 }
 
                 // If specific members defined, check member is of one of those
@@ -118,7 +118,7 @@ namespace Umbraco.Cms.Web.Common.Security
         /// <inheritdoc />
         public bool IsLoggedIn()
         {
-            HttpContext httpContext = _httpContextAccessor.HttpContext;
+            HttpContext? httpContext = _httpContextAccessor.HttpContext;
             return httpContext?.User.Identity?.IsAuthenticated ?? false;
         }
 
@@ -169,7 +169,7 @@ namespace Umbraco.Cms.Web.Common.Security
         }
 
         /// <inheritdoc />
-        public async Task<MemberIdentityUser> GetCurrentMemberAsync()
+        public async Task<MemberIdentityUser?> GetCurrentMemberAsync()
         {
             if (_currentMember == null)
             {
@@ -177,7 +177,7 @@ namespace Umbraco.Cms.Web.Common.Security
                 {
                     return null;
                 }
-                _currentMember = await GetUserAsync(_httpContextAccessor.HttpContext.User);
+                _currentMember = await GetUserAsync(_httpContextAccessor.HttpContext?.User);
             }
             return _currentMember;
         }
@@ -190,7 +190,7 @@ namespace Umbraco.Cms.Web.Common.Security
         /// <returns></returns>
         private async Task<bool> HasAccessAsync(string path)
         {
-            MemberIdentityUser currentMember = await GetCurrentMemberAsync();
+            MemberIdentityUser? currentMember = await GetCurrentMemberAsync();
             if (currentMember == null || !currentMember.IsApproved || currentMember.IsLockedOut)
             {
                 return false;
@@ -205,7 +205,7 @@ namespace Umbraco.Cms.Web.Common.Security
         private async Task<IReadOnlyDictionary<string, bool>> HasAccessAsync(IEnumerable<string> paths)
         {
             var result = new Dictionary<string, bool>();
-            MemberIdentityUser currentMember = await GetCurrentMemberAsync();
+            MemberIdentityUser? currentMember = await GetCurrentMemberAsync();
 
             if (currentMember == null || !currentMember.IsApproved || currentMember.IsLockedOut)
             {
@@ -213,7 +213,7 @@ namespace Umbraco.Cms.Web.Common.Security
             }
 
             // ensure we only lookup user roles once
-            IList<string> userRoles = null;
+            IList<string>? userRoles = null;
             async Task<IList<string>> getUserRolesAsync()
             {
                 if (userRoles != null)
@@ -235,6 +235,6 @@ namespace Umbraco.Cms.Web.Common.Security
             return result;
         }
 
-        public IPublishedContent AsPublishedMember(MemberIdentityUser user) => _store.GetPublishedMember(user);
+        public IPublishedContent? AsPublishedMember(MemberIdentityUser user) => _store.GetPublishedMember(user);
     }
 }
diff --git a/src/Umbraco.Web.Common/Security/MemberSignInManager.cs b/src/Umbraco.Web.Common/Security/MemberSignInManager.cs
index e8bf1c2eb3..2710dc38c1 100644
--- a/src/Umbraco.Web.Common/Security/MemberSignInManager.cs
+++ b/src/Umbraco.Web.Common/Security/MemberSignInManager.cs
@@ -70,7 +70,7 @@ namespace Umbraco.Cms.Web.Common.Security
         protected override string TwoFactorRememberMeAuthenticationType => IdentityConstants.TwoFactorRememberMeScheme;
 
         /// <inheritdoc />
-        public override async Task<ExternalLoginInfo> GetExternalLoginInfoAsync(string expectedXsrf = null)
+        public override async Task<ExternalLoginInfo?> GetExternalLoginInfoAsync(string? expectedXsrf = null)
         {
             // borrowed from https://github.com/dotnet/aspnetcore/blob/master/src/Identity/Core/src/SignInManager.cs#L422
             // to replace the auth scheme
@@ -111,7 +111,7 @@ namespace Umbraco.Cms.Web.Common.Security
             var providerDisplayName = (await GetExternalAuthenticationSchemesAsync()).FirstOrDefault(p => p.Name == provider)?.DisplayName ?? provider;
             return new ExternalLoginInfo(auth.Principal, provider, providerKey, providerDisplayName)
             {
-                AuthenticationTokens = auth.Properties.GetTokens(),
+                AuthenticationTokens = auth.Properties?.GetTokens(),
                 AuthenticationProperties = auth.Properties
             };
         }
@@ -157,7 +157,7 @@ namespace Umbraco.Cms.Web.Common.Security
         /// <param name="loginInfo"></param>
         /// <param name="autoLinkOptions"></param>
         /// <returns></returns>
-        private async Task<SignInResult> AutoLinkAndSignInExternalAccount(ExternalLoginInfo loginInfo, MemberExternalSignInAutoLinkOptions autoLinkOptions)
+        private async Task<SignInResult> AutoLinkAndSignInExternalAccount(ExternalLoginInfo loginInfo, MemberExternalSignInAutoLinkOptions? autoLinkOptions)
         {
             // If there are no autolink options then the attempt is failed (user does not exist)
             if (autoLinkOptions == null || !autoLinkOptions.AutoLinkExternalAccount)
@@ -295,7 +295,7 @@ namespace Umbraco.Cms.Web.Common.Security
         }
 
         /// <inheritdoc />
-        public override AuthenticationProperties ConfigureExternalAuthenticationProperties(string provider, string redirectUrl, string userId = null)
+        public override AuthenticationProperties ConfigureExternalAuthenticationProperties(string provider, string redirectUrl, string? userId = null)
         {
             // borrowed from https://github.com/dotnet/aspnetcore/blob/master/src/Identity/Core/src/SignInManager.cs
             // to be able to use our own XsrfKey/LoginProviderKey because the default is private :/
@@ -354,7 +354,7 @@ namespace Umbraco.Cms.Web.Common.Security
             Logger.LogWarning("The AutoLinkOptions of the external authentication provider '{LoginProvider}' have refused the login based on the OnExternalLogin method. Affected user id: '{UserId}'", loginInfo.LoginProvider, user.Id);
 
         protected override async Task<SignInResult> SignInOrTwoFactorAsync(MemberIdentityUser user, bool isPersistent,
-            string loginProvider = null, bool bypassTwoFactor = false)
+            string? loginProvider = null, bool bypassTwoFactor = false)
         {
             var result = await base.SignInOrTwoFactorAsync(user, isPersistent, loginProvider, bypassTwoFactor);
 
diff --git a/src/Umbraco.Web.Common/Security/UmbracoSignInManager.cs b/src/Umbraco.Web.Common/Security/UmbracoSignInManager.cs
index cc07b6bd28..8e276b57a6 100644
--- a/src/Umbraco.Web.Common/Security/UmbracoSignInManager.cs
+++ b/src/Umbraco.Web.Common/Security/UmbracoSignInManager.cs
@@ -51,7 +51,7 @@ namespace Umbraco.Cms.Web.Common.Security
         }
 
         /// <inheritdoc />
-        public override async Task<ExternalLoginInfo> GetExternalLoginInfoAsync(string expectedXsrf = null)
+        public override async Task<ExternalLoginInfo?> GetExternalLoginInfoAsync(string? expectedXsrf = null)
         {
             // borrowed from https://github.com/dotnet/aspnetcore/blob/master/src/Identity/Core/src/SignInManager.cs#L422
             // to replace the auth scheme
@@ -91,7 +91,7 @@ namespace Umbraco.Cms.Web.Common.Security
             var providerDisplayName = (await GetExternalAuthenticationSchemesAsync()).FirstOrDefault(p => p.Name == provider)?.DisplayName ?? provider;
             return new ExternalLoginInfo(auth.Principal, provider, providerKey, providerDisplayName)
             {
-                AuthenticationTokens = auth.Properties.GetTokens(),
+                AuthenticationTokens = auth.Properties?.GetTokens(),
                 AuthenticationProperties = auth.Properties
             };
         }
@@ -105,7 +105,7 @@ namespace Umbraco.Cms.Web.Common.Security
             var info = await RetrieveTwoFactorInfoAsync();
             if (info == null)
             {
-                return null;
+                return null!;
             }
             return await UserManager.FindByIdAsync(info.UserId);
         }
@@ -198,7 +198,7 @@ namespace Umbraco.Cms.Web.Common.Security
         }
 
         /// <inheritdoc />
-        public override async Task SignInWithClaimsAsync(TUser user, AuthenticationProperties authenticationProperties, IEnumerable<Claim> additionalClaims)
+        public override async Task SignInWithClaimsAsync(TUser user, AuthenticationProperties? authenticationProperties, IEnumerable<Claim> additionalClaims)
         {
             // override to replace IdentityConstants.ApplicationScheme with custom AuthenticationType
             // code taken from aspnetcore: https://github.com/dotnet/aspnetcore/blob/master/src/Identity/Core/src/SignInManager.cs
@@ -308,7 +308,7 @@ namespace Umbraco.Cms.Web.Common.Security
         /// <param name="username"></param>
         /// <param name="result"></param>
         /// <returns></returns>
-        protected virtual async Task<SignInResult> HandleSignIn(TUser user, string username, SignInResult result)
+        protected virtual async Task<SignInResult> HandleSignIn(TUser? user, string? username, SignInResult result)
         {
             // TODO: Here I believe we can do all (or most) of the usermanager event raising so that it is not in the AuthenticationController
 
@@ -320,7 +320,7 @@ namespace Umbraco.Cms.Web.Common.Security
             if (result.Succeeded)
             {
                 //track the last login date
-                user.LastLoginDateUtc = DateTime.UtcNow;
+                user!.LastLoginDateUtc = DateTime.UtcNow;
                 if (user.AccessFailedCount > 0)
                 {
                     //we have successfully logged in, reset the AccessFailedCount
@@ -351,7 +351,7 @@ namespace Umbraco.Cms.Web.Common.Security
         }
 
         /// <inheritdoc />
-        protected override async Task<SignInResult> SignInOrTwoFactorAsync(TUser user, bool isPersistent, string loginProvider = null, bool bypassTwoFactor = false)
+        protected override async Task<SignInResult> SignInOrTwoFactorAsync(TUser user, bool isPersistent, string? loginProvider = null, bool bypassTwoFactor = false)
         {
             // borrowed from https://github.com/dotnet/aspnetcore/blob/master/src/Identity/Core/src/SignInManager.cs
             // to replace custom auth types
@@ -391,7 +391,7 @@ namespace Umbraco.Cms.Web.Common.Security
 
         // borrowed from https://github.com/dotnet/aspnetcore/blob/master/src/Identity/Core/src/SignInManager.cs#L743
         // to replace custom auth types
-        private ClaimsPrincipal StoreTwoFactorInfo(string userId, string loginProvider)
+        private ClaimsPrincipal StoreTwoFactorInfo(string userId, string? loginProvider)
         {
             var identity = new ClaimsIdentity(TwoFactorAuthenticationType);
             identity.AddClaim(new Claim(ClaimTypes.Name, userId));
@@ -419,7 +419,7 @@ namespace Umbraco.Cms.Web.Common.Security
 
         // borrowed from https://github.com/dotnet/aspnetcore/blob/master/src/Identity/Core/src/SignInManager.cs
         // copy is required in order to use a custom auth type
-        private async Task<TwoFactorAuthenticationInfo> RetrieveTwoFactorInfoAsync()
+        private async Task<TwoFactorAuthenticationInfo?> RetrieveTwoFactorInfoAsync()
         {
             var result = await Context.AuthenticateAsync(TwoFactorAuthenticationType);
             if (result?.Principal != null)
@@ -463,8 +463,8 @@ namespace Umbraco.Cms.Web.Common.Security
         // borrowed from https://github.com/dotnet/aspnetcore/blob/master/src/Identity/Core/src/SignInManager.cs#L891
         private class TwoFactorAuthenticationInfo
         {
-            public string UserId { get; set; }
-            public string LoginProvider { get; set; }
+            public string? UserId { get; set; }
+            public string? LoginProvider { get; set; }
         }
     }
 }
diff --git a/src/Umbraco.Web.Common/Templates/TemplateRenderer.cs b/src/Umbraco.Web.Common/Templates/TemplateRenderer.cs
index 92ec2fa962..46d5856c9d 100644
--- a/src/Umbraco.Web.Common/Templates/TemplateRenderer.cs
+++ b/src/Umbraco.Web.Common/Templates/TemplateRenderer.cs
@@ -93,7 +93,7 @@ namespace Umbraco.Cms.Web.Common.Templates
 
                 requestBuilder.SetCulture(defaultLanguage == null
                     ? CultureInfo.CurrentUICulture.Name
-                    : defaultLanguage.CultureInfo.Name);
+                    : defaultLanguage.CultureInfo?.Name);
             }
             else
             {
@@ -130,7 +130,7 @@ namespace Umbraco.Cms.Web.Common.Templates
 
             // First, save all of the items locally that we know are used in the chain of execution, we'll need to restore these
             // after this page has rendered.
-            SaveExistingItems(out IPublishedRequest oldPublishedRequest);
+            SaveExistingItems(out IPublishedRequest? oldPublishedRequest);
 
             IPublishedRequest contentRequest = requestBuilder.Build();
 
@@ -199,7 +199,7 @@ namespace Umbraco.Cms.Web.Common.Templates
         /// <summary>
         /// Save all items that we know are used for rendering execution to variables so we can restore after rendering
         /// </summary>
-        private void SaveExistingItems(out IPublishedRequest oldPublishedRequest)
+        private void SaveExistingItems(out IPublishedRequest? oldPublishedRequest)
         {
             var umbracoContext = _umbracoContextAccessor.GetRequiredUmbracoContext();
             // Many objects require that these legacy items are in the http context items... before we render this template we need to first
@@ -210,7 +210,7 @@ namespace Umbraco.Cms.Web.Common.Templates
         /// <summary>
         /// Restores all items back to their context's to continue normal page rendering execution
         /// </summary>
-        private void RestoreItems(IPublishedRequest oldPublishedRequest)
+        private void RestoreItems(IPublishedRequest? oldPublishedRequest)
         {
             var umbracoContext = _umbracoContextAccessor.GetRequiredUmbracoContext();
             umbracoContext.PublishedRequest = oldPublishedRequest;
diff --git a/src/Umbraco.Web.Common/UmbracoContext/UmbracoContext.cs b/src/Umbraco.Web.Common/UmbracoContext/UmbracoContext.cs
index cc56526d72..98f3db5483 100644
--- a/src/Umbraco.Web.Common/UmbracoContext/UmbracoContext.cs
+++ b/src/Umbraco.Web.Common/UmbracoContext/UmbracoContext.cs
@@ -20,12 +20,12 @@ namespace Umbraco.Cms.Web.Common.UmbracoContext
         private readonly ICookieManager _cookieManager;
         private readonly IHttpContextAccessor _httpContextAccessor;
         private readonly Lazy<IPublishedSnapshot> _publishedSnapshot;
-        private string _previewToken;
+        private string? _previewToken;
         private bool? _previewing;
         private readonly UmbracoRequestPaths _umbracoRequestPaths;
-        private Uri _requestUrl;
-        private Uri _originalRequestUrl;
-        private Uri _cleanedUmbracoUrl;
+        private Uri? _requestUrl;
+        private Uri? _originalRequestUrl;
+        private Uri? _cleanedUmbracoUrl;
 
         // initializes a new instance of the UmbracoContext class
         // internal for unit tests
@@ -67,7 +67,7 @@ namespace Umbraco.Cms.Web.Common.UmbracoContext
         internal Guid UmbracoRequestId { get; }
 
         // lazily get/create a Uri for the current request
-        private Uri RequestUrl => _requestUrl ??= _httpContextAccessor.HttpContext is null
+        private Uri? RequestUrl => _requestUrl ??= _httpContextAccessor.HttpContext is null
             ? null
             : new Uri(_httpContextAccessor.HttpContext.Request.GetEncodedUrl());
 
@@ -94,16 +94,16 @@ namespace Umbraco.Cms.Web.Common.UmbracoContext
         public IPublishedMediaCache Media => PublishedSnapshot.Media;
 
         /// <inheritdoc/>
-        public IDomainCache Domains => PublishedSnapshot.Domains;
+        public IDomainCache? Domains => PublishedSnapshot.Domains;
 
         /// <inheritdoc/>
-        public IPublishedRequest PublishedRequest { get; set; }
+        public IPublishedRequest? PublishedRequest { get; set; }
 
         /// <inheritdoc/>
         public bool IsDebug => // NOTE: the request can be null during app startup!
                 _hostingEnvironment.IsDebugMode
-                       && (string.IsNullOrEmpty(_httpContextAccessor.HttpContext.GetRequestValue("umbdebugshowtrace")) == false
-                           || string.IsNullOrEmpty(_httpContextAccessor.HttpContext.GetRequestValue("umbdebug")) == false
+                       && (string.IsNullOrEmpty(_httpContextAccessor.HttpContext?.GetRequestValue("umbdebugshowtrace")) == false
+                           || string.IsNullOrEmpty(_httpContextAccessor.HttpContext?.GetRequestValue("umbdebug")) == false
                            || string.IsNullOrEmpty(_cookieManager.GetCookieValue("UMB-DEBUG")) == false);
 
         /// <inheritdoc/>
@@ -121,7 +121,7 @@ namespace Umbraco.Cms.Web.Common.UmbracoContext
             private set => _previewing = value;
         }
 
-        internal string PreviewToken
+        internal string? PreviewToken
         {
             get
             {
diff --git a/src/Umbraco.Web.Common/UmbracoHelper.cs b/src/Umbraco.Web.Common/UmbracoHelper.cs
index 98f2d08fdd..c7e29a7302 100644
--- a/src/Umbraco.Web.Common/UmbracoHelper.cs
+++ b/src/Umbraco.Web.Common/UmbracoHelper.cs
@@ -24,8 +24,8 @@ namespace Umbraco.Cms.Web.Common
         private readonly IUmbracoComponentRenderer _componentRenderer;
         private readonly ICultureDictionaryFactory _cultureDictionaryFactory;
 
-        private IPublishedContent _currentPage;
-        private ICultureDictionary _cultureDictionary;
+        private IPublishedContent? _currentPage;
+        private ICultureDictionary? _cultureDictionary;
 
         #region Constructors
 
@@ -50,7 +50,9 @@ namespace Umbraco.Cms.Web.Common
         /// Initializes a new empty instance of <see cref="UmbracoHelper"/>.
         /// </summary>
         /// <remarks>For tests - nothing is initialized.</remarks>
+#pragma warning disable CS8618
         internal UmbracoHelper()
+#pragma warning restore CS8618
         { }
 
         #endregion
@@ -137,7 +139,7 @@ namespace Umbraco.Cms.Web.Common
         /// </summary>
         /// <param name="key"></param>
         /// <returns></returns>
-        public string GetDictionaryValue(string key)
+        public string? GetDictionaryValue(string key)
         {
             return CultureDictionary[key];
         }
@@ -174,12 +176,12 @@ namespace Umbraco.Cms.Web.Common
         /// </summary>
         /// <param name="id">The unique identifier, or the key, of the content item.</param>
         /// <returns>The content, or null of the content item is not in the cache.</returns>
-        public IPublishedContent Content(object id)
+        public IPublishedContent? Content(object id)
         {
             return ContentForObject(id);
         }
 
-        private IPublishedContent ContentForObject(object id) => _publishedContentQuery.Content(id);
+        private IPublishedContent? ContentForObject(object id) => _publishedContentQuery.Content(id);
 
         public IPublishedContent ContentSingleAtXPath(string xpath, params XPathVariable[] vars)
         {
@@ -191,7 +193,7 @@ namespace Umbraco.Cms.Web.Common
         /// </summary>
         /// <param name="id">The unique identifier of the content item.</param>
         /// <returns>The content, or null of the content item is not in the cache.</returns>
-        public IPublishedContent Content(int id) => _publishedContentQuery.Content(id);
+        public IPublishedContent? Content(int id) => _publishedContentQuery.Content(id);
 
         /// <summary>
         /// Gets a content item from the cache.
@@ -205,9 +207,9 @@ namespace Umbraco.Cms.Web.Common
         /// </summary>
         /// <param name="id">The unique identifier, or the key, of the content item.</param>
         /// <returns>The content, or null of the content item is not in the cache.</returns>
-        public IPublishedContent Content(string id) => _publishedContentQuery.Content(id);
+        public IPublishedContent? Content(string id) => _publishedContentQuery.Content(id);
 
-        public IPublishedContent Content(Udi id) => _publishedContentQuery.Content(id);
+        public IPublishedContent? Content(Udi id) => _publishedContentQuery.Content(id);
 
         /// <summary>
         /// Gets content items from the cache.
@@ -318,7 +320,7 @@ namespace Umbraco.Cms.Web.Common
         #endregion
         #region Media
 
-        public IPublishedContent Media(Udi id) => _publishedContentQuery.Media(id);
+        public IPublishedContent? Media(Udi id) => _publishedContentQuery.Media(id);
 
         public IPublishedContent Media(Guid id) => _publishedContentQuery.Media(id);
 
@@ -332,16 +334,16 @@ namespace Umbraco.Cms.Web.Common
         /// this result in to this method.
         /// This method will throw an exception if the value is not of type int or string.
         /// </remarks>
-        public IPublishedContent Media(object id)
+        public IPublishedContent? Media(object id)
         {
             return MediaForObject(id);
         }
 
-        private IPublishedContent MediaForObject(object id) => _publishedContentQuery.Media(id);
+        private IPublishedContent? MediaForObject(object id) => _publishedContentQuery.Media(id);
 
-        public IPublishedContent Media(int id) => _publishedContentQuery.Media(id);
+        public IPublishedContent? Media(int id) => _publishedContentQuery.Media(id);
 
-        public IPublishedContent Media(string id) => _publishedContentQuery.Media(id);
+        public IPublishedContent? Media(string id) => _publishedContentQuery.Media(id);
 
         /// <summary>
         /// Gets the medias corresponding to the identifiers.
diff --git a/src/Umbraco.Web.Common/UmbracoHelperAccessor.cs b/src/Umbraco.Web.Common/UmbracoHelperAccessor.cs
index 926e1e1d72..70f609d1c0 100644
--- a/src/Umbraco.Web.Common/UmbracoHelperAccessor.cs
+++ b/src/Umbraco.Web.Common/UmbracoHelperAccessor.cs
@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
@@ -14,7 +15,7 @@ namespace Umbraco.Cms.Web.Common
 
         public UmbracoHelperAccessor(IHttpContextAccessor httpContextAccessor) => _httpContextAccessor = httpContextAccessor;
 
-        public bool TryGetUmbracoHelper(out UmbracoHelper umbracoHelper)
+        public bool TryGetUmbracoHelper([MaybeNullWhen(false)] out UmbracoHelper umbracoHelper)
         {
             umbracoHelper = _httpContextAccessor.HttpContext?.RequestServices.GetService<UmbracoHelper>();
             return umbracoHelper is not null;
diff --git a/src/Umbraco.Web.Common/Views/UmbracoViewPage.cs b/src/Umbraco.Web.Common/Views/UmbracoViewPage.cs
index d9bed99861..7351a278fb 100644
--- a/src/Umbraco.Web.Common/Views/UmbracoViewPage.cs
+++ b/src/Umbraco.Web.Common/Views/UmbracoViewPage.cs
@@ -27,8 +27,8 @@ namespace Umbraco.Cms.Web.Common.Views
 
     public abstract class UmbracoViewPage<TModel> : RazorPage<TModel>
     {
-        private IUmbracoContext _umbracoContext;
-        private UmbracoHelper _helper;
+        private IUmbracoContext? _umbracoContext;
+        private UmbracoHelper? _helper;
 
         private IUmbracoContextAccessor UmbracoContextAccessor => Context.RequestServices.GetRequiredService<IUmbracoContextAccessor>();
 
@@ -53,7 +53,7 @@ namespace Umbraco.Cms.Web.Common.Views
                     return _helper;
                 }
 
-                TModel model = ViewData.Model;
+                TModel? model = ViewData.Model;
                 var content = model as IPublishedContent;
                 if (content is null && model is IContentModel contentModel)
                 {
@@ -78,7 +78,7 @@ namespace Umbraco.Cms.Web.Common.Views
         /// <summary>
         /// Gets the <see cref="IUmbracoContext"/>
         /// </summary>
-        protected IUmbracoContext UmbracoContext
+        protected IUmbracoContext? UmbracoContext
         {
             get
             {
@@ -86,6 +86,7 @@ namespace Umbraco.Cms.Web.Common.Views
                 {
                     return null;
                 }
+
                 return umbracoContext;
             }
         }
@@ -104,7 +105,7 @@ namespace Umbraco.Cms.Web.Common.Views
         }
 
         /// <inheritdoc/>
-        public override void Write(object value)
+        public override void Write(object? value)
         {
             if (value is IHtmlEncodedString htmlEncodedString)
             {
@@ -128,7 +129,7 @@ namespace Umbraco.Cms.Web.Common.Views
             // ASP.NET default value is text/html
             if (Context.Response?.ContentType?.InvariantContains("text/html") ?? false)
             {
-                if ((UmbracoContext.IsDebug || UmbracoContext.InPreviewMode)
+                if (((UmbracoContext?.IsDebug ?? false) || (UmbracoContext?.InPreviewMode ?? false))
                     && tagHelperOutput.TagName != null
                     && tagHelperOutput.TagName.Equals("body", StringComparison.InvariantCultureIgnoreCase))
                 {
@@ -142,7 +143,7 @@ namespace Umbraco.Cms.Web.Common.Views
                                 ContentSettings.PreviewBadge,
                                 IOHelper.ResolveUrl(GlobalSettings.UmbracoPath),
                                 Context.Request.GetEncodedUrl(),
-                                UmbracoContext.PublishedRequest.PublishedContent.Id);
+                                UmbracoContext.PublishedRequest?.PublishedContent?.Id);
                     }
                     else
                     {
@@ -163,7 +164,7 @@ namespace Umbraco.Cms.Web.Common.Views
         /// <see cref="IContentModel"/> or <see cref="IPublishedContent"/>. This will use the <see cref="ContentModelBinder"/> to bind the models
         /// to the correct output type.
         /// </remarks>
-        protected ViewDataDictionary BindViewData(ContentModelBinder contentModelBinder, ViewDataDictionary viewData)
+        protected ViewDataDictionary BindViewData(ContentModelBinder contentModelBinder, ViewDataDictionary? viewData)
         {
             if (contentModelBinder is null)
             {
@@ -187,8 +188,8 @@ namespace Umbraco.Cms.Web.Common.Views
             if (viewData.ModelMetadata.ModelType == typeof(ContentModel)
                 && typeof(TModel) == typeof(IPublishedContent))
             {
-                var contentModel = (ContentModel)viewData.Model;
-                viewData.Model = contentModel.Content;
+                var contentModel = (ContentModel?)viewData.Model;
+                viewData.Model = contentModel?.Content;
                 return viewData;
             }
 
@@ -202,7 +203,7 @@ namespace Umbraco.Cms.Web.Common.Views
             var bindingContext = new DefaultModelBindingContext();
             contentModelBinder.BindModel(bindingContext, viewDataModel, typeof(TModel));
 
-            viewData.Model = bindingContext.Result.Model;
+            viewData!.Model = bindingContext.Result.Model;
 
             // return the new view data
             return (ViewDataDictionary<TModel>)viewData;
@@ -211,7 +212,7 @@ namespace Umbraco.Cms.Web.Common.Views
         // viewData is the ViewDataDictionary (maybe <TModel>) that we have
         // modelType is the type of the model that we need to bind to
         // figure out whether viewData can accept modelType else replace it
-        private static ViewDataDictionary MapViewDataDictionary(ViewDataDictionary viewData, Type modelType)
+        private static ViewDataDictionary? MapViewDataDictionary(ViewDataDictionary viewData, Type modelType)
         {
             Type viewDataType = viewData.GetType();
 
@@ -239,19 +240,19 @@ namespace Umbraco.Cms.Web.Common.Views
             // if not possible or it is not generic then we need to create a new ViewDataDictionary
             Type nViewDataType = typeof(ViewDataDictionary<>).MakeGenericType(modelType);
             var tViewData = new ViewDataDictionary(viewData) { Model = default(TModel) }; // temp view data to copy values
-            var nViewData = (ViewDataDictionary)Activator.CreateInstance(nViewDataType, tViewData);
+            var nViewData = (ViewDataDictionary?)Activator.CreateInstance(nViewDataType, tViewData);
             return nViewData;
         }
 
         /// <summary>
         /// Renders a section with default content if the section isn't defined
         /// </summary>
-        public HtmlString RenderSection(string name, HtmlString defaultContents) => RazorPageExtensions.RenderSection(this, name, defaultContents);
+        public HtmlString? RenderSection(string name, HtmlString defaultContents) => RazorPageExtensions.RenderSection(this, name, defaultContents);
 
         /// <summary>
         /// Renders a section with default content if the section isn't defined
         /// </summary>
-        public HtmlString RenderSection(string name, string defaultContents) => RazorPageExtensions.RenderSection(this, name, defaultContents);
+        public HtmlString? RenderSection(string name, string defaultContents) => RazorPageExtensions.RenderSection(this, name, defaultContents);
 
     }
 }