diff --git a/src/Umbraco.Core/Cache/AppCacheExtensions.cs b/src/Umbraco.Core/Cache/AppCacheExtensions.cs
index d41f1119ed..f5e92cc116 100644
--- a/src/Umbraco.Core/Cache/AppCacheExtensions.cs
+++ b/src/Umbraco.Core/Cache/AppCacheExtensions.cs
@@ -31,7 +31,7 @@ namespace Umbraco.Extensions
             provider.Insert(cacheKey, () => getCacheItem(), timeout, isSliding, dependentFiles);
         }
 
-        public static IEnumerable<T>? GetCacheItemsByKeySearch<T>(this IAppCache provider, string keyStartsWith)
+        public static IEnumerable<T?> GetCacheItemsByKeySearch<T>(this IAppCache provider, string keyStartsWith)
         {
             var result = provider.SearchByKey(keyStartsWith);
             return result.Select(x => x.TryConvertTo<T>().Result);
diff --git a/src/Umbraco.Core/Cache/JsonCacheRefresherBase.cs b/src/Umbraco.Core/Cache/JsonCacheRefresherBase.cs
index 92669159f1..a6b705ae5d 100644
--- a/src/Umbraco.Core/Cache/JsonCacheRefresherBase.cs
+++ b/src/Umbraco.Core/Cache/JsonCacheRefresherBase.cs
@@ -44,7 +44,7 @@ namespace Umbraco.Cms.Core.Cache
         /// </summary>
         /// <param name="json">The json payload.</param>
         /// <returns>The deserialized object payload.</returns>
-        public TJsonPayload[] Deserialize(string json)
+        public TJsonPayload[]? Deserialize(string json)
         {
             return JsonSerializer.Deserialize<TJsonPayload[]>(json);
         }
diff --git a/src/Umbraco.Core/Cache/NoCacheRepositoryCachePolicy.cs b/src/Umbraco.Core/Cache/NoCacheRepositoryCachePolicy.cs
index 7c912d5c22..e01f7b2458 100644
--- a/src/Umbraco.Core/Cache/NoCacheRepositoryCachePolicy.cs
+++ b/src/Umbraco.Core/Cache/NoCacheRepositoryCachePolicy.cs
@@ -12,7 +12,7 @@ namespace Umbraco.Cms.Core.Cache
 
         public static NoCacheRepositoryCachePolicy<TEntity, TId> Instance { get; } = new NoCacheRepositoryCachePolicy<TEntity, TId>();
 
-        public TEntity Get(TId id, Func<TId, TEntity> performGet, Func<TId[], IEnumerable<TEntity>> performGetAll)
+        public TEntity? Get(TId? id, Func<TId?, TEntity?> performGet, Func<TId[]?, IEnumerable<TEntity>?> performGetAll)
         {
             return performGet(id);
         }
@@ -22,7 +22,7 @@ namespace Umbraco.Cms.Core.Cache
             return null;
         }
 
-        public bool Exists(TId id, Func<TId, bool> performExists, Func<TId[], IEnumerable<TEntity>> performGetAll)
+        public bool Exists(TId id, Func<TId, bool> performExists, Func<TId[], IEnumerable<TEntity>?> performGetAll)
         {
             return performExists(id);
         }
@@ -42,9 +42,9 @@ namespace Umbraco.Cms.Core.Cache
             persistDeleted(entity);
         }
 
-        public TEntity?[] GetAll(TId[] ids, Func<TId[], IEnumerable<TEntity?>> performGetAll)
+        public TEntity[]? GetAll(TId[]? ids, Func<TId[]?, IEnumerable<TEntity>?> performGetAll)
         {
-            return performGetAll(ids).ToArray();
+            return performGetAll(ids)?.ToArray();
         }
 
         public void ClearAll()
diff --git a/src/Umbraco.Core/Configuration/Grid/GridEditorsConfig.cs b/src/Umbraco.Core/Configuration/Grid/GridEditorsConfig.cs
index 3abc688c01..db5d669ce9 100644
--- a/src/Umbraco.Core/Configuration/Grid/GridEditorsConfig.cs
+++ b/src/Umbraco.Core/Configuration/Grid/GridEditorsConfig.cs
@@ -45,7 +45,7 @@ namespace Umbraco.Cms.Core.Configuration.Grid
 
                         try
                         {
-                            editors.AddRange(_jsonSerializer.Deserialize<IEnumerable<GridEditor>>(sourceString));
+                            editors.AddRange(_jsonSerializer.Deserialize<IEnumerable<GridEditor>>(sourceString)!);
                         }
                         catch (Exception ex)
                         {
@@ -62,7 +62,7 @@ namespace Umbraco.Cms.Core.Configuration.Grid
                         {
                             using var reader = new StreamReader(resourceStream, Encoding.UTF8);
                             var sourceString = reader.ReadToEnd();
-                            editors.AddRange(_jsonSerializer.Deserialize<IEnumerable<GridEditor>>(sourceString));
+                            editors.AddRange(_jsonSerializer.Deserialize<IEnumerable<GridEditor>>(sourceString)!);
                         }
                     }
 
diff --git a/src/Umbraco.Core/Events/UserNotificationsHandler.cs b/src/Umbraco.Core/Events/UserNotificationsHandler.cs
index 61ac33a5c0..61bcde6a1b 100644
--- a/src/Umbraco.Core/Events/UserNotificationsHandler.cs
+++ b/src/Umbraco.Core/Events/UserNotificationsHandler.cs
@@ -217,22 +217,22 @@ namespace Umbraco.Cms.Core.Events
 
         public void Handle(AssignedUserGroupPermissionsNotification notification)
         {
-            var entities = _contentService.GetByIds(notification.EntityPermissions.Select(e => e.EntityId)).ToArray();
-            if (entities.Any() == false)
+            var entities = _contentService.GetByIds(notification.EntityPermissions.Select(e => e.EntityId))?.ToArray();
+            if (entities?.Any() == false)
             {
                 return;
             }
-            _notifier.Notify(_actions.GetAction<ActionRights>(), entities);
+            _notifier.Notify(_actions.GetAction<ActionRights>(), entities!);
         }
 
         public void Handle(PublicAccessEntrySavedNotification notification)
         {
-            var entities = _contentService.GetByIds(notification.SavedEntities.Select(e => e.ProtectedNodeId)).ToArray();
-            if (entities.Any() == false)
+            var entities = _contentService.GetByIds(notification.SavedEntities.Select(e => e.ProtectedNodeId))?.ToArray();
+            if (entities?.Any() == false)
             {
                 return;
             }
-            _notifier.Notify(_actions.GetAction<ActionProtect>(), entities);
+            _notifier.Notify(_actions.GetAction<ActionProtect>(), entities!);
         }
     }
 }
diff --git a/src/Umbraco.Core/Extensions/ClaimsIdentityExtensions.cs b/src/Umbraco.Core/Extensions/ClaimsIdentityExtensions.cs
index d1d71a9ca1..27331d31a5 100644
--- a/src/Umbraco.Core/Extensions/ClaimsIdentityExtensions.cs
+++ b/src/Umbraco.Core/Extensions/ClaimsIdentityExtensions.cs
@@ -150,8 +150,8 @@ namespace Umbraco.Extensions
         /// <param name="allowedApps">Allowed apps</param>
         /// <param name="roles">Roles</param>
         public static void AddRequiredClaims(this ClaimsIdentity identity, string userId, string username,
-            string? realName, IEnumerable<int>? startContentNodes, IEnumerable<int>? startMediaNodes, string culture,
-            string securityStamp, IEnumerable<string> allowedApps, IEnumerable<string?> roles)
+            string realName, IEnumerable<int>? startContentNodes, IEnumerable<int>? startMediaNodes, string culture,
+            string securityStamp, IEnumerable<string> allowedApps, IEnumerable<string> roles)
         {
             //This is the id that 'identity' uses to check for the user id
             if (identity.HasClaim(x => x.Type == ClaimTypes.NameIdentifier) == false)
diff --git a/src/Umbraco.Core/IO/IFileSystem.cs b/src/Umbraco.Core/IO/IFileSystem.cs
index 853b91f663..232827300c 100644
--- a/src/Umbraco.Core/IO/IFileSystem.cs
+++ b/src/Umbraco.Core/IO/IFileSystem.cs
@@ -97,7 +97,7 @@ namespace Umbraco.Cms.Core.IO
         /// <returns>
         /// <c>True</c> if the file exists and the user has permission to view it; otherwise <c>false</c>.
         /// </returns>
-        bool FileExists(string? path);
+        bool FileExists(string path);
 
         /// <summary>
         /// Returns the application relative path to the file.
diff --git a/src/Umbraco.Core/Install/InstallStatusTracker.cs b/src/Umbraco.Core/Install/InstallStatusTracker.cs
index 43e2f477a4..1ee7f685d4 100644
--- a/src/Umbraco.Core/Install/InstallStatusTracker.cs
+++ b/src/Umbraco.Core/Install/InstallStatusTracker.cs
@@ -66,9 +66,12 @@ namespace Umbraco.Cms.Core.Install
             {
                 var deserialized = _jsonSerializer.Deserialize<IEnumerable<InstallTrackingItem>>(
                     File.ReadAllText(file));
-                foreach (var item in deserialized)
+                if (deserialized is not null)
                 {
-                    _steps.Add(item);
+                    foreach (var item in deserialized)
+                    {
+                        _steps.Add(item);
+                    }
                 }
             }
             else
@@ -89,9 +92,12 @@ namespace Umbraco.Cms.Core.Install
                 {
                     var deserialized = _jsonSerializer.Deserialize<IEnumerable<InstallTrackingItem>>(
                         File.ReadAllText(file));
-                    foreach (var item in deserialized)
+                    if (deserialized is not null)
                     {
-                        _steps.Add(item);
+                        foreach (var item in deserialized)
+                        {
+                            _steps.Add(item);
+                        }
                     }
                 }
                 else
diff --git a/src/Umbraco.Core/Install/InstallSteps/UpgradeStep.cs b/src/Umbraco.Core/Install/InstallSteps/UpgradeStep.cs
index 93290cc249..6530983de2 100644
--- a/src/Umbraco.Core/Install/InstallSteps/UpgradeStep.cs
+++ b/src/Umbraco.Core/Install/InstallSteps/UpgradeStep.cs
@@ -29,7 +29,7 @@ namespace Umbraco.Cms.Core.Install.InstallSteps
         {
             get
             {
-                string FormatGuidState(string value)
+                string FormatGuidState(string? value)
                 {
                     if (string.IsNullOrWhiteSpace(value)) value = "unknown";
                     else if (Guid.TryParse(value, out var currentStateGuid))
diff --git a/src/Umbraco.Core/Macros/IMacroRenderer.cs b/src/Umbraco.Core/Macros/IMacroRenderer.cs
index 473959f94f..bac3d36268 100644
--- a/src/Umbraco.Core/Macros/IMacroRenderer.cs
+++ b/src/Umbraco.Core/Macros/IMacroRenderer.cs
@@ -9,6 +9,6 @@ namespace Umbraco.Cms.Core.Macros
     /// </summary>
     public interface IMacroRenderer
     {
-        Task<MacroContent> RenderAsync(string macroAlias, IPublishedContent? content, IDictionary<string, object> macroParams);
+        Task<MacroContent> RenderAsync(string macroAlias, IPublishedContent? content, IDictionary<string, object?>? macroParams);
     }
 }
diff --git a/src/Umbraco.Core/Manifest/IManifestParser.cs b/src/Umbraco.Core/Manifest/IManifestParser.cs
index 14e3d01cca..09d3ccbe1c 100644
--- a/src/Umbraco.Core/Manifest/IManifestParser.cs
+++ b/src/Umbraco.Core/Manifest/IManifestParser.cs
@@ -10,7 +10,7 @@ namespace Umbraco.Cms.Core.Manifest
         /// Gets all manifests, merged into a single manifest object.
         /// </summary>
         /// <returns></returns>
-        CompositePackageManifest? CombinedManifest { get; }
+        CompositePackageManifest CombinedManifest { get; }
 
         /// <summary>
         /// Parses a manifest.
diff --git a/src/Umbraco.Core/Manifest/PackageManifest.cs b/src/Umbraco.Core/Manifest/PackageManifest.cs
index 14ff1165cd..a71cf1f6f6 100644
--- a/src/Umbraco.Core/Manifest/PackageManifest.cs
+++ b/src/Umbraco.Core/Manifest/PackageManifest.cs
@@ -19,7 +19,7 @@ namespace Umbraco.Cms.Core.Manifest
         /// An optional package name. If not specified then the directory name is used.
         /// </summary>
         [DataMember(Name = "name")]
-        public string PackageName
+        public string? PackageName
         {
             get
             {
diff --git a/src/Umbraco.Core/Mapping/MapperContext.cs b/src/Umbraco.Core/Mapping/MapperContext.cs
index 4bc4455e67..2e128e2475 100644
--- a/src/Umbraco.Core/Mapping/MapperContext.cs
+++ b/src/Umbraco.Core/Mapping/MapperContext.cs
@@ -37,7 +37,7 @@ namespace Umbraco.Cms.Core.Mapping
         /// <typeparam name="TTarget">The target type.</typeparam>
         /// <param name="source">The source object.</param>
         /// <returns>The target object.</returns>
-        public TTarget Map<TTarget>(object source)
+        public TTarget? Map<TTarget>(object source)
             => _mapper.Map<TTarget>(source, this);
 
         // let's say this is a bad (dangerous) idea, and leave it out for now
@@ -63,7 +63,7 @@ namespace Umbraco.Cms.Core.Mapping
         /// <typeparam name="TTarget">The target type.</typeparam>
         /// <param name="source">The source object.</param>
         /// <returns>The target object.</returns>
-        public TTarget Map<TSource, TTarget>(TSource? source)
+        public TTarget? Map<TSource, TTarget>(TSource? source)
             => _mapper.Map<TSource, TTarget>(source, this);
 
         // let's say this is a bad (dangerous) idea, and leave it out for now
diff --git a/src/Umbraco.Core/Media/EmbedProviders/OEmbedProviderBase.cs b/src/Umbraco.Core/Media/EmbedProviders/OEmbedProviderBase.cs
index 7fafc232df..31ea975164 100644
--- a/src/Umbraco.Core/Media/EmbedProviders/OEmbedProviderBase.cs
+++ b/src/Umbraco.Core/Media/EmbedProviders/OEmbedProviderBase.cs
@@ -61,7 +61,7 @@ namespace Umbraco.Cms.Core.Media.EmbedProviders
             }
         }
 
-        public virtual T GetJsonResponse<T>(string url) where T : class
+        public virtual T? GetJsonResponse<T>(string url) where T : class
         {
             var response = DownloadResponse(url);
             return _jsonSerializer.Deserialize<T>(response);
diff --git a/src/Umbraco.Core/Models/DictionaryItem.cs b/src/Umbraco.Core/Models/DictionaryItem.cs
index 359d6de01c..14cd3bb2e5 100644
--- a/src/Umbraco.Core/Models/DictionaryItem.cs
+++ b/src/Umbraco.Core/Models/DictionaryItem.cs
@@ -75,7 +75,7 @@ namespace Umbraco.Cms.Core.Models
                     }
                 }
 
-                SetPropertyValueAndDetectChanges(asArray, ref _translations, nameof(Translations),
+                SetPropertyValueAndDetectChanges(asArray, ref _translations!, nameof(Translations),
                     DictionaryTranslationComparer);
             }
         }
diff --git a/src/Umbraco.Core/Models/DictionaryTranslation.cs b/src/Umbraco.Core/Models/DictionaryTranslation.cs
index 11b1229206..d0d98a64db 100644
--- a/src/Umbraco.Core/Models/DictionaryTranslation.cs
+++ b/src/Umbraco.Core/Models/DictionaryTranslation.cs
@@ -14,11 +14,11 @@ namespace Umbraco.Cms.Core.Models
         public Func<int, ILanguage?>? GetLanguage { get; set; }
 
         private ILanguage? _language;
-        private string? _value;
+        private string _value;
         //note: this will be memberwise cloned
         private int _languageId;
 
-        public DictionaryTranslation(ILanguage language, string? value)
+        public DictionaryTranslation(ILanguage language, string value)
         {
             if (language == null) throw new ArgumentNullException("language");
             _language = language;
@@ -88,10 +88,10 @@ namespace Umbraco.Cms.Core.Models
         /// Gets or sets the translated text
         /// </summary>
         [DataMember]
-        public string? Value
+        public string Value
         {
             get { return _value; }
-            set { SetPropertyValueAndDetectChanges(value, ref _value, nameof(Value)); }
+            set { SetPropertyValueAndDetectChanges(value, ref _value!, nameof(Value)); }
         }
 
         protected override void PerformDeepClone(object clone)
diff --git a/src/Umbraco.Core/Models/Email/NotificationEmailModel.cs b/src/Umbraco.Core/Models/Email/NotificationEmailModel.cs
index f27b279c80..c71519d83f 100644
--- a/src/Umbraco.Core/Models/Email/NotificationEmailModel.cs
+++ b/src/Umbraco.Core/Models/Email/NotificationEmailModel.cs
@@ -8,19 +8,19 @@ namespace Umbraco.Cms.Core.Models.Email
     /// </summary>
     public class NotificationEmailModel
     {
-        public NotificationEmailAddress From { get; }
+        public NotificationEmailAddress? From { get; }
 
-        public IEnumerable<NotificationEmailAddress> To { get; }
+        public IEnumerable<NotificationEmailAddress?>? To { get; }
 
-        public IEnumerable<NotificationEmailAddress> Cc { get; }
+        public IEnumerable<NotificationEmailAddress>? Cc { get; }
 
-        public IEnumerable<NotificationEmailAddress> Bcc { get; }
+        public IEnumerable<NotificationEmailAddress>? Bcc { get; }
 
-        public IEnumerable<NotificationEmailAddress> ReplyTo { get; }
+        public IEnumerable<NotificationEmailAddress>? ReplyTo { get; }
 
-        public string Subject { get; }
+        public string? Subject { get; }
 
-        public string Body { get; }
+        public string? Body { get; }
 
         public bool IsBodyHtml { get; }
 
diff --git a/src/Umbraco.Core/Models/Entities/ITreeEntity.cs b/src/Umbraco.Core/Models/Entities/ITreeEntity.cs
index b970f46726..0024a7cdc4 100644
--- a/src/Umbraco.Core/Models/Entities/ITreeEntity.cs
+++ b/src/Umbraco.Core/Models/Entities/ITreeEntity.cs
@@ -8,7 +8,7 @@
         /// <summary>
         /// Gets or sets the name of the entity.
         /// </summary>
-        string Name { get; set; }
+        string? Name { get; set; }
 
         /// <summary>
         /// Gets or sets the identifier of the user who created this entity.
diff --git a/src/Umbraco.Core/Models/Entities/TreeEntityBase.cs b/src/Umbraco.Core/Models/Entities/TreeEntityBase.cs
index 54befb1f1f..de54009ccd 100644
--- a/src/Umbraco.Core/Models/Entities/TreeEntityBase.cs
+++ b/src/Umbraco.Core/Models/Entities/TreeEntityBase.cs
@@ -23,7 +23,7 @@ namespace Umbraco.Cms.Core.Models.Entities
         public string? Name
         {
             get => _name;
-            set => SetPropertyValueAndDetectChanges(value, ref _name!, nameof(Name));
+            set => SetPropertyValueAndDetectChanges(value, ref _name, nameof(Name));
         }
 
         /// <inheritdoc />
diff --git a/src/Umbraco.Core/Models/ILanguage.cs b/src/Umbraco.Core/Models/ILanguage.cs
index d392e2bb37..fc20642464 100644
--- a/src/Umbraco.Core/Models/ILanguage.cs
+++ b/src/Umbraco.Core/Models/ILanguage.cs
@@ -19,7 +19,7 @@ namespace Umbraco.Cms.Core.Models
         /// Gets or sets the culture name of the language.
         /// </summary>
         [DataMember]
-        string CultureName { get; set; }
+        string? CultureName { get; set; }
 
         /// <summary>
         /// Gets the <see cref="CultureInfo"/> object for the language.
diff --git a/src/Umbraco.Core/Models/IRedirectUrl.cs b/src/Umbraco.Core/Models/IRedirectUrl.cs
index 18498837b4..f2e4e131a7 100644
--- a/src/Umbraco.Core/Models/IRedirectUrl.cs
+++ b/src/Umbraco.Core/Models/IRedirectUrl.cs
@@ -38,7 +38,7 @@ namespace Umbraco.Cms.Core.Models
         /// </summary>
         /// <remarks>Is a proper Umbraco route eg /path/to/foo or 123/path/tofoo.</remarks>
         [DataMember]
-        string Url { get; set; }
+        string? Url { get; set; }
 
     }
 }
diff --git a/src/Umbraco.Core/Models/Macro.cs b/src/Umbraco.Core/Models/Macro.cs
index bccb1bbb83..1e395c2158 100644
--- a/src/Umbraco.Core/Models/Macro.cs
+++ b/src/Umbraco.Core/Models/Macro.cs
@@ -27,6 +27,7 @@ namespace Umbraco.Cms.Core.Models
             _properties.CollectionChanged += PropertiesChanged;
             _addedProperties = new List<string>();
             _removedProperties = new List<string>();
+            _macroSource = string.Empty;
         }
 
         /// <summary>
@@ -69,7 +70,7 @@ namespace Umbraco.Cms.Core.Models
         /// <param name="dontRender"></param>
         /// <param name="macroSource"></param>
         public Macro(IShortStringHelper shortStringHelper, string @alias, string? name,
-            string? macroSource,
+            string macroSource,
             bool cacheByPage = false,
             bool cacheByMember = false,
             bool dontRender = true,
@@ -94,7 +95,7 @@ namespace Umbraco.Cms.Core.Models
         private bool _cacheByPage;
         private bool _cacheByMember;
         private bool _dontRender;
-        private string? _macroSource;
+        private string _macroSource;
         private MacroPropertyCollection _properties;
         private List<string> _addedProperties;
         private List<string> _removedProperties;
@@ -245,10 +246,10 @@ namespace Umbraco.Cms.Core.Models
         /// Gets or set the path to the Partial View to render
         /// </summary>
         [DataMember]
-        public string? MacroSource
+        public string MacroSource
         {
             get => _macroSource;
-            set => SetPropertyValueAndDetectChanges(value, ref _macroSource, nameof(MacroSource));
+            set => SetPropertyValueAndDetectChanges(value, ref _macroSource!, nameof(MacroSource));
         }
 
         /// <summary>
diff --git a/src/Umbraco.Core/Models/Membership/User.cs b/src/Umbraco.Core/Models/Membership/User.cs
index f5a4a87db7..91ef03bd4a 100644
--- a/src/Umbraco.Core/Models/Membership/User.cs
+++ b/src/Umbraco.Core/Models/Membership/User.cs
@@ -32,6 +32,7 @@ namespace Umbraco.Cms.Core.Models.Membership
             _rawPasswordValue = "";
             _username = string.Empty;
             _email = string.Empty;
+            _name = string.Empty;
         }
 
         /// <summary>
@@ -72,7 +73,7 @@ namespace Umbraco.Cms.Core.Models.Membership
         /// <param name="userGroups"></param>
         /// <param name="startContentIds"></param>
         /// <param name="startMediaIds"></param>
-        public User(GlobalSettings globalSettings, int id, string? name, string? email, string? username,
+        public User(GlobalSettings globalSettings, int id, string? name, string email, string? username,
             string? rawPasswordValue, string? passwordConfig,
             IEnumerable<IReadOnlyUserGroup> userGroups, int[] startContentIds, int[] startMediaIds)
             : this(globalSettings)
@@ -98,7 +99,7 @@ namespace Umbraco.Cms.Core.Models.Membership
             _startMediaIds = startMediaIds;
         }
 
-        private string? _name;
+        private string _name;
         private string? _securityStamp;
         private string? _avatar;
         private string? _tourData;
@@ -111,7 +112,7 @@ namespace Umbraco.Cms.Core.Models.Membership
         private DateTime? _emailConfirmedDate;
         private DateTime? _invitedDate;
         private string _email;
-        private string _rawPasswordValue;
+        private string? _rawPasswordValue;
         private string? _passwordConfig;
         private IEnumerable<string>? _allowedSections;
         private HashSet<IReadOnlyUserGroup> _userGroups;
@@ -158,7 +159,7 @@ namespace Umbraco.Cms.Core.Models.Membership
         }
 
         [IgnoreDataMember]
-        public string RawPasswordValue
+        public string? RawPasswordValue
         {
             get => _rawPasswordValue;
             set => SetPropertyValueAndDetectChanges(value, ref _rawPasswordValue, nameof(RawPasswordValue));
@@ -237,10 +238,10 @@ namespace Umbraco.Cms.Core.Models.Membership
         }
 
         [DataMember]
-        public string? Name
+        public string Name
         {
             get => _name;
-            set => SetPropertyValueAndDetectChanges(value, ref _name, nameof(Name));
+            set => SetPropertyValueAndDetectChanges(value, ref _name!, nameof(Name));
         }
 
         public IEnumerable<string> AllowedSections
diff --git a/src/Umbraco.Core/Models/Packaging/CompiledPackage.cs b/src/Umbraco.Core/Models/Packaging/CompiledPackage.cs
index 34f4f83755..4497d6be4d 100644
--- a/src/Umbraco.Core/Models/Packaging/CompiledPackage.cs
+++ b/src/Umbraco.Core/Models/Packaging/CompiledPackage.cs
@@ -10,8 +10,8 @@ namespace Umbraco.Cms.Core.Models.Packaging
     /// </summary>
     public class CompiledPackage
     {
-        public FileInfo PackageFile { get; set; } = null!;
-        public string Name { get; set; } = string.Empty;
+        public FileInfo? PackageFile { get; set; }
+        public string? Name { get; set; }
         public InstallWarnings Warnings { get; set; } = new InstallWarnings();
         public IEnumerable<XElement> Macros { get; set; } = null!; // TODO: make strongly typed
         public IEnumerable<XElement> MacroPartialViews { get; set; } = null!; // TODO: make strongly typed
diff --git a/src/Umbraco.Core/Models/PropertyCollection.cs b/src/Umbraco.Core/Models/PropertyCollection.cs
index 4dc4bc05a0..9a8daac0c4 100644
--- a/src/Umbraco.Core/Models/PropertyCollection.cs
+++ b/src/Umbraco.Core/Models/PropertyCollection.cs
@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
 using System.Collections.Specialized;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Runtime.Serialization;
 using Umbraco.Extensions;
@@ -145,7 +146,7 @@ namespace Umbraco.Cms.Core.Models
             }
         }
 
-        public bool TryGetValue(string propertyTypeAlias, out IProperty? property)
+        public bool TryGetValue(string propertyTypeAlias, [MaybeNullWhen(false)] out IProperty property)
         {
             property = this.FirstOrDefault(x => x.Alias?.InvariantEquals(propertyTypeAlias) ?? false);
             return property != null;
diff --git a/src/Umbraco.Core/Models/PropertyTagsExtensions.cs b/src/Umbraco.Core/Models/PropertyTagsExtensions.cs
index 66716876e9..ebcf073a63 100644
--- a/src/Umbraco.Core/Models/PropertyTagsExtensions.cs
+++ b/src/Umbraco.Core/Models/PropertyTagsExtensions.cs
@@ -25,7 +25,7 @@ namespace Umbraco.Extensions
             var tagAttribute = editor?.GetTagAttribute();
             if (tagAttribute == null) return null;
 
-            var configurationObject = property.PropertyType is null ? null : dataTypeService.GetDataType(property.PropertyType.DataTypeId).Configuration;
+            var configurationObject = property.PropertyType is null ? null : dataTypeService.GetDataType(property.PropertyType.DataTypeId)?.Configuration;
             var configuration = ConfigurationEditor.ConfigurationAs<TagConfiguration>(configurationObject);
 
             if (configuration?.Delimiter == default && configuration?.Delimiter is not null)
@@ -165,7 +165,7 @@ namespace Umbraco.Extensions
                 case TagsStorageType.Json:
                     try
                     {
-                        return serializer.Deserialize<string[]>(value).Select(x => x.Trim());
+                        return serializer.Deserialize<string[]>(value)?.Select(x => x.Trim()) ?? Enumerable.Empty<string>();
                     }
                     catch (Exception)
                     {
diff --git a/src/Umbraco.Core/Models/PropertyType.cs b/src/Umbraco.Core/Models/PropertyType.cs
index d8a71f4cfa..3acbad2720 100644
--- a/src/Umbraco.Core/Models/PropertyType.cs
+++ b/src/Umbraco.Core/Models/PropertyType.cs
@@ -89,6 +89,7 @@ namespace Umbraco.Cms.Core.Models
             _forceValueStorageType = forceValueStorageType;
             _alias = propertyTypeAlias == null ? string.Empty : SanitizeAlias(propertyTypeAlias);
             _variations = ContentVariation.Nothing;
+            _name = string.Empty;
         }
 
         /// <summary>
diff --git a/src/Umbraco.Core/Models/PublishedContent/NoopPublishedModelFactory.cs b/src/Umbraco.Core/Models/PublishedContent/NoopPublishedModelFactory.cs
index d3f97a893d..f53a5236a9 100644
--- a/src/Umbraco.Core/Models/PublishedContent/NoopPublishedModelFactory.cs
+++ b/src/Umbraco.Core/Models/PublishedContent/NoopPublishedModelFactory.cs
@@ -12,7 +12,7 @@ namespace Umbraco.Cms.Core.Models.PublishedContent
         public IPublishedElement CreateModel(IPublishedElement element) => element;
 
         /// <inheritdoc />
-        public IList CreateModelList(string alias) => new List<IPublishedElement>();
+        public IList CreateModelList(string? alias) => new List<IPublishedElement>();
 
         /// <inheritdoc />
         public Type MapModelType(Type type) => typeof(IPublishedElement);
diff --git a/src/Umbraco.Core/Models/PublishedContent/PublishedContentTypeFactory.cs b/src/Umbraco.Core/Models/PublishedContent/PublishedContentTypeFactory.cs
index 31a05123b1..accbbab6e2 100644
--- a/src/Umbraco.Core/Models/PublishedContent/PublishedContentTypeFactory.cs
+++ b/src/Umbraco.Core/Models/PublishedContent/PublishedContentTypeFactory.cs
@@ -78,19 +78,19 @@ namespace Umbraco.Cms.Core.Models.PublishedContent
         /// <inheritdoc />
         public PublishedDataType GetDataType(int id)
         {
-            Dictionary<int, PublishedDataType> publishedDataTypes;
+            Dictionary<int, PublishedDataType>? publishedDataTypes;
             lock (_publishedDataTypesLocker)
             {
                 if (_publishedDataTypes == null)
                 {
                     var dataTypes = _dataTypeService.GetAll();
-                    _publishedDataTypes = dataTypes.ToDictionary(x => x.Id, CreatePublishedDataType);
+                    _publishedDataTypes = dataTypes?.ToDictionary(x => x.Id, CreatePublishedDataType);
                 }
 
                 publishedDataTypes = _publishedDataTypes;
             }
 
-            if (!publishedDataTypes.TryGetValue(id, out var dataType))
+            if (publishedDataTypes is null || !publishedDataTypes.TryGetValue(id, out var dataType))
                 throw new ArgumentException($"Could not find a datatype with identifier {id}.", nameof(id));
 
             return dataType;
@@ -104,7 +104,7 @@ namespace Umbraco.Cms.Core.Models.PublishedContent
                 if (_publishedDataTypes == null)
                 {
                     var dataTypes = _dataTypeService.GetAll();
-                    _publishedDataTypes = dataTypes.ToDictionary(x => x.Id, CreatePublishedDataType);
+                    _publishedDataTypes = dataTypes?.ToDictionary(x => x.Id, CreatePublishedDataType);
                 }
                 else
                 {
@@ -112,8 +112,11 @@ namespace Umbraco.Cms.Core.Models.PublishedContent
                         _publishedDataTypes.Remove(id);
 
                     var dataTypes = _dataTypeService.GetAll(ids);
-                    foreach (var dataType in dataTypes)
-                        _publishedDataTypes[dataType.Id] = CreatePublishedDataType(dataType);
+                    if (dataTypes is not null)
+                    {
+                        foreach (var dataType in dataTypes)
+                            _publishedDataTypes[dataType.Id] = CreatePublishedDataType(dataType);
+                    }
                 }
             }
         }
diff --git a/src/Umbraco.Core/Models/PublishedContent/PublishedModelFactory.cs b/src/Umbraco.Core/Models/PublishedContent/PublishedModelFactory.cs
index 3c8ae6b3d2..2d40874b57 100644
--- a/src/Umbraco.Core/Models/PublishedContent/PublishedModelFactory.cs
+++ b/src/Umbraco.Core/Models/PublishedContent/PublishedModelFactory.cs
@@ -104,13 +104,13 @@ namespace Umbraco.Cms.Core.Models.PublishedContent
         }
 
         /// <inheritdoc />
-        public IList? CreateModelList(string alias)
+        public IList? CreateModelList(string? alias)
         {
             // fail fast
             if (_modelInfos == null)
                 return new List<IPublishedElement>();
 
-            if (!_modelInfos.TryGetValue(alias, out var modelInfo) || modelInfo.ModelType is null)
+            if (alias is null || !_modelInfos.TryGetValue(alias, out var modelInfo) || modelInfo.ModelType is null)
                 return new List<IPublishedElement>();
 
             var ctor = modelInfo.ListCtor;
diff --git a/src/Umbraco.Core/Models/PublishedContent/PublishedPropertyType.cs b/src/Umbraco.Core/Models/PublishedContent/PublishedPropertyType.cs
index 002848a758..9420811f24 100644
--- a/src/Umbraco.Core/Models/PublishedContent/PublishedPropertyType.cs
+++ b/src/Umbraco.Core/Models/PublishedContent/PublishedPropertyType.cs
@@ -240,12 +240,12 @@ namespace Umbraco.Cms.Core.Models.PublishedContent
         }
 
         /// <inheritdoc />
-        public Type? ModelClrType
+        public Type ModelClrType
         {
             get
             {
                 if (!_initialized) Initialize();
-                return _modelClrType;
+                return _modelClrType!;
             }
         }
 
diff --git a/src/Umbraco.Core/Models/Relation.cs b/src/Umbraco.Core/Models/Relation.cs
index 7cb447ccc3..54227db910 100644
--- a/src/Umbraco.Core/Models/Relation.cs
+++ b/src/Umbraco.Core/Models/Relation.cs
@@ -14,7 +14,7 @@ namespace Umbraco.Cms.Core.Models
         //NOTE: The datetime column from umbracoRelation is set on CreateDate on the Entity
         private int _parentId;
         private int _childId;
-        private IRelationType? _relationType;
+        private IRelationType _relationType;
         private string? _comment;
 
         /// <summary>
@@ -38,7 +38,7 @@ namespace Umbraco.Cms.Core.Models
         /// <param name="parentObjectType"></param>
         /// <param name="childObjectType"></param>
         /// <param name="relationType"></param>
-        public Relation(int parentId, int childId, Guid parentObjectType, Guid childObjectType, IRelationType? relationType)
+        public Relation(int parentId, int childId, Guid parentObjectType, Guid childObjectType, IRelationType relationType)
         {
             _parentId = parentId;
             _childId = childId;
diff --git a/src/Umbraco.Core/Models/Tag.cs b/src/Umbraco.Core/Models/Tag.cs
index 428f9583d0..92436d068b 100644
--- a/src/Umbraco.Core/Models/Tag.cs
+++ b/src/Umbraco.Core/Models/Tag.cs
@@ -11,8 +11,8 @@ namespace Umbraco.Cms.Core.Models
     [DataContract(IsReference = true)]
     public class Tag : EntityBase, ITag
     {
-        private string? _group;
-        private string? _text;
+        private string _group = string.Empty;
+        private string _text = string.Empty;
         private int? _languageId;
 
         /// <summary>
@@ -24,7 +24,7 @@ namespace Umbraco.Cms.Core.Models
         /// <summary>
         /// Initializes a new instance of the <see cref="Tag"/> class.
         /// </summary>
-        public Tag(int id, string? group, string? text, int? languageId = null)
+        public Tag(int id, string group, string text, int? languageId = null)
         {
             Id = id;
             Text = text;
@@ -33,17 +33,17 @@ namespace Umbraco.Cms.Core.Models
         }
 
         /// <inheritdoc />
-        public string? Group
+        public string Group
         {
             get => _group;
-            set => SetPropertyValueAndDetectChanges(value, ref _group, nameof(Group));
+            set => SetPropertyValueAndDetectChanges(value, ref _group!, nameof(Group));
         }
 
         /// <inheritdoc />
-        public string? Text
+        public string Text
         {
             get => _text;
-            set => SetPropertyValueAndDetectChanges(value, ref _text, nameof(Text));
+            set => SetPropertyValueAndDetectChanges(value, ref _text!, nameof(Text));
         }
 
         /// <inheritdoc />
diff --git a/src/Umbraco.Core/Models/UserExtensions.cs b/src/Umbraco.Core/Models/UserExtensions.cs
index ba63780975..4d0fefd16c 100644
--- a/src/Umbraco.Core/Models/UserExtensions.cs
+++ b/src/Umbraco.Core/Models/UserExtensions.cs
@@ -25,7 +25,7 @@ namespace Umbraco.Cms.Core.Models
         /// <returns>
         /// A list of 5 different sized avatar URLs
         /// </returns>
-        public static string[] GetUserAvatarUrls(this IUser user, IAppCache cache, MediaFileManager mediaFileManager, IImageUrlGenerator imageUrlGenerator)
+        public static string?[] GetUserAvatarUrls(this IUser user, IAppCache cache, MediaFileManager mediaFileManager, IImageUrlGenerator imageUrlGenerator)
         {
             // If FIPS is required, never check the Gravatar service as it only supports MD5 hashing.
             // Unfortunately, if the FIPS setting is enabled on Windows, using MD5 will throw an exception
diff --git a/src/Umbraco.Core/Notifications/ContentEmptyingRecycleBinNotification.cs b/src/Umbraco.Core/Notifications/ContentEmptyingRecycleBinNotification.cs
index f66400a9a8..134e65d982 100644
--- a/src/Umbraco.Core/Notifications/ContentEmptyingRecycleBinNotification.cs
+++ b/src/Umbraco.Core/Notifications/ContentEmptyingRecycleBinNotification.cs
@@ -9,7 +9,7 @@ namespace Umbraco.Cms.Core.Notifications
 {
     public sealed class ContentEmptyingRecycleBinNotification : EmptyingRecycleBinNotification<IContent>
     {
-        public ContentEmptyingRecycleBinNotification(IEnumerable<IContent> deletedEntities, EventMessages messages) : base(deletedEntities, messages)
+        public ContentEmptyingRecycleBinNotification(IEnumerable<IContent>? deletedEntities, EventMessages messages) : base(deletedEntities, messages)
         {
         }
     }
diff --git a/src/Umbraco.Core/Notifications/EmptyingRecycleBinNotification.cs b/src/Umbraco.Core/Notifications/EmptyingRecycleBinNotification.cs
index 3d1732acfa..42005fc9f4 100644
--- a/src/Umbraco.Core/Notifications/EmptyingRecycleBinNotification.cs
+++ b/src/Umbraco.Core/Notifications/EmptyingRecycleBinNotification.cs
@@ -8,13 +8,13 @@ namespace Umbraco.Cms.Core.Notifications
 {
     public abstract class EmptyingRecycleBinNotification<T> : StatefulNotification, ICancelableNotification where T : class
     {
-        protected EmptyingRecycleBinNotification(IEnumerable<T> deletedEntities, EventMessages messages)
+        protected EmptyingRecycleBinNotification(IEnumerable<T>? deletedEntities, EventMessages messages)
         {
             DeletedEntities = deletedEntities;
             Messages = messages;
         }
 
-        public IEnumerable<T> DeletedEntities { get; }
+        public IEnumerable<T>? DeletedEntities { get; }
 
         public EventMessages Messages { get; }
 
diff --git a/src/Umbraco.Core/Notifications/IStatefulNotification.cs b/src/Umbraco.Core/Notifications/IStatefulNotification.cs
index 7fa2382038..87d2b58cde 100644
--- a/src/Umbraco.Core/Notifications/IStatefulNotification.cs
+++ b/src/Umbraco.Core/Notifications/IStatefulNotification.cs
@@ -4,6 +4,6 @@ namespace Umbraco.Cms.Core.Notifications
 {
     public interface IStatefulNotification : INotification
     {
-        IDictionary<string, object> State { get; set; }
+        IDictionary<string, object>? State { get; set; }
     }
 }
diff --git a/src/Umbraco.Core/Persistence/IReadRepository.cs b/src/Umbraco.Core/Persistence/IReadRepository.cs
index 57a25f3f81..0f757ae04a 100644
--- a/src/Umbraco.Core/Persistence/IReadRepository.cs
+++ b/src/Umbraco.Core/Persistence/IReadRepository.cs
@@ -15,7 +15,7 @@ namespace Umbraco.Cms.Core.Persistence
         /// <summary>
         /// Gets entities.
         /// </summary>
-        IEnumerable<TEntity>? GetMany(params TId[]? ids);
+        IEnumerable<TEntity> GetMany(params TId[]? ids);
 
         /// <summary>
         /// Gets a value indicating whether an entity exists.
diff --git a/src/Umbraco.Core/Persistence/SqlExtensionsStatics.cs b/src/Umbraco.Core/Persistence/SqlExtensionsStatics.cs
index cec65de33f..d0f32fb971 100644
--- a/src/Umbraco.Core/Persistence/SqlExtensionsStatics.cs
+++ b/src/Umbraco.Core/Persistence/SqlExtensionsStatics.cs
@@ -16,7 +16,7 @@ namespace Umbraco.Cms.Core.Persistence
         /// </summary>
         /// <param name="field">The field to alias.</param>
         /// <param name="alias">The alias.</param>
-        public static object Alias(object? field, string alias) => field;
+        public static object? Alias(object? field, string alias) => field;
 
         /// <summary>
         /// Produces Sql text.
diff --git a/src/Umbraco.Core/PropertyEditors/ConfigurationEditor.cs b/src/Umbraco.Core/PropertyEditors/ConfigurationEditor.cs
index 5384ef0813..ef441d3965 100644
--- a/src/Umbraco.Core/PropertyEditors/ConfigurationEditor.cs
+++ b/src/Umbraco.Core/PropertyEditors/ConfigurationEditor.cs
@@ -83,7 +83,7 @@ namespace Umbraco.Cms.Core.PropertyEditors
         public virtual object FromDatabase(string? configurationJson, IConfigurationEditorJsonSerializer configurationEditorJsonSerializer)
             => string.IsNullOrWhiteSpace(configurationJson)
                 ? new Dictionary<string, object>()
-                : configurationEditorJsonSerializer.Deserialize<Dictionary<string, object>>(configurationJson);
+                : configurationEditorJsonSerializer.Deserialize<Dictionary<string, object>>(configurationJson)!;
 
         /// <inheritdoc />
         public virtual object? FromConfigurationEditor(IDictionary<string, object> editorValues, object configuration)
diff --git a/src/Umbraco.Core/PropertyEditors/DataValueEditor.cs b/src/Umbraco.Core/PropertyEditors/DataValueEditor.cs
index 888c74ff29..ab84f7131b 100644
--- a/src/Umbraco.Core/PropertyEditors/DataValueEditor.cs
+++ b/src/Umbraco.Core/PropertyEditors/DataValueEditor.cs
@@ -24,16 +24,16 @@ namespace Umbraco.Cms.Core.PropertyEditors
     [DataContract]
     public class DataValueEditor : IDataValueEditor
     {
-        private readonly ILocalizedTextService? _localizedTextService;
-        private readonly IShortStringHelper? _shortStringHelper;
+        private readonly ILocalizedTextService _localizedTextService;
+        private readonly IShortStringHelper _shortStringHelper;
         private readonly IJsonSerializer? _jsonSerializer;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="DataValueEditor"/> class.
         /// </summary>
         public DataValueEditor(
-            ILocalizedTextService? localizedTextService,
-            IShortStringHelper? shortStringHelper,
+            ILocalizedTextService localizedTextService,
+            IShortStringHelper shortStringHelper,
             IJsonSerializer? jsonSerializer) // for tests, and manifest
         {
             _localizedTextService = localizedTextService;
@@ -167,9 +167,9 @@ namespace Umbraco.Cms.Core.PropertyEditors
             // Ensure JSON is serialized properly (without indentation or converted to null when empty)
             if (value is not null && ValueType.InvariantEquals(ValueTypes.Json))
             {
-                var jsonValue = _jsonSerializer.Serialize(value);
+                var jsonValue = _jsonSerializer?.Serialize(value);
 
-                if (jsonValue.DetectIsEmptyJson())
+                if (jsonValue?.DetectIsEmptyJson() ?? false)
                 {
                     value = null;
                 }
@@ -231,7 +231,7 @@ namespace Umbraco.Cms.Core.PropertyEditors
         /// If overridden then the object returned must match the type supplied in the ValueType, otherwise persisting the
         /// value to the DB will fail when it tries to validate the value type.
         /// </remarks>
-        public virtual object? FromEditor(ContentPropertyData editorValue, object currentValue)
+        public virtual object? FromEditor(ContentPropertyData editorValue, object? currentValue)
         {
             var result = TryConvertValueToCrlType(editorValue.Value);
             if (result.Success == false)
@@ -274,7 +274,7 @@ namespace Umbraco.Cms.Core.PropertyEditors
                     {
                         try
                         {
-                            var json = _jsonSerializer.Deserialize<dynamic>(stringValue!);
+                            var json = _jsonSerializer?.Deserialize<dynamic>(stringValue!);
                             return json;
                         }
                         catch
diff --git a/src/Umbraco.Core/PropertyEditors/DataValueEditorFactory.cs b/src/Umbraco.Core/PropertyEditors/DataValueEditorFactory.cs
index 300bdde672..1f717d9065 100644
--- a/src/Umbraco.Core/PropertyEditors/DataValueEditorFactory.cs
+++ b/src/Umbraco.Core/PropertyEditors/DataValueEditorFactory.cs
@@ -10,9 +10,9 @@ namespace Umbraco.Cms.Core.PropertyEditors
 
         public DataValueEditorFactory(IServiceProvider serviceProvider) => _serviceProvider = serviceProvider;
 
-        public TDataValueEditor Create<TDataValueEditor>(params object[] args)
+        public TDataValueEditor Create<TDataValueEditor>(params object?[] args)
          where TDataValueEditor: class, IDataValueEditor
-            => _serviceProvider.CreateInstance<TDataValueEditor>(args);
+            => _serviceProvider.CreateInstance<TDataValueEditor>(args.WhereNotNull());
 
     }
 }
diff --git a/src/Umbraco.Core/PropertyEditors/DefaultPropertyIndexValueFactory.cs b/src/Umbraco.Core/PropertyEditors/DefaultPropertyIndexValueFactory.cs
index 78061a1be4..5cb11b7071 100644
--- a/src/Umbraco.Core/PropertyEditors/DefaultPropertyIndexValueFactory.cs
+++ b/src/Umbraco.Core/PropertyEditors/DefaultPropertyIndexValueFactory.cs
@@ -10,7 +10,7 @@ namespace Umbraco.Cms.Core.PropertyEditors
     public class DefaultPropertyIndexValueFactory : IPropertyIndexValueFactory
     {
         /// <inheritdoc />
-        public IEnumerable<KeyValuePair<string, IEnumerable<object?>>> GetIndexValues(IProperty property, string culture, string segment, bool published)
+        public IEnumerable<KeyValuePair<string, IEnumerable<object?>>> GetIndexValues(IProperty property, string? culture, string? segment, bool published)
         {
             yield return new KeyValuePair<string, IEnumerable<object?>>(
                 property.Alias,
diff --git a/src/Umbraco.Core/PropertyEditors/MediaPicker3Configuration.cs b/src/Umbraco.Core/PropertyEditors/MediaPicker3Configuration.cs
index 50595b7350..8b843fdf85 100644
--- a/src/Umbraco.Core/PropertyEditors/MediaPicker3Configuration.cs
+++ b/src/Umbraco.Core/PropertyEditors/MediaPicker3Configuration.cs
@@ -46,7 +46,7 @@ namespace Umbraco.Cms.Core.PropertyEditors
         public class CropConfiguration
         {
             [DataMember(Name = "alias")]
-            public string Alias { get; set; }
+            public string? Alias { get; set; }
 
             [DataMember(Name = "label")]
             public string? Label { get; set; }
diff --git a/src/Umbraco.Core/PropertyEditors/ValueConverters/CheckboxListValueConverter.cs b/src/Umbraco.Core/PropertyEditors/ValueConverters/CheckboxListValueConverter.cs
index 0e89770956..2aeee98bf4 100644
--- a/src/Umbraco.Core/PropertyEditors/ValueConverters/CheckboxListValueConverter.cs
+++ b/src/Umbraco.Core/PropertyEditors/ValueConverters/CheckboxListValueConverter.cs
@@ -26,7 +26,7 @@ namespace Umbraco.Cms.Core.PropertyEditors.ValueConverters
         public override PropertyCacheLevel GetPropertyCacheLevel(IPublishedPropertyType propertyType)
             => PropertyCacheLevel.Element;
 
-        public override object ConvertIntermediateToObject(IPublishedElement owner, IPublishedPropertyType propertyType, PropertyCacheLevel cacheLevel, object? source, bool preview)
+        public override object? ConvertIntermediateToObject(IPublishedElement owner, IPublishedPropertyType propertyType, PropertyCacheLevel cacheLevel, object? source, bool preview)
         {
             var sourceString = source?.ToString() ?? string.Empty;
 
diff --git a/src/Umbraco.Core/PropertyEditors/ValueConverters/SliderValueConverter.cs b/src/Umbraco.Core/PropertyEditors/ValueConverters/SliderValueConverter.cs
index c0293a0241..1da3458dab 100644
--- a/src/Umbraco.Core/PropertyEditors/ValueConverters/SliderValueConverter.cs
+++ b/src/Umbraco.Core/PropertyEditors/ValueConverters/SliderValueConverter.cs
@@ -71,7 +71,7 @@ namespace Umbraco.Cms.Core.PropertyEditors.ValueConverters
             return Storages.GetOrAdd(dataTypeId, id =>
             {
                 var dataType = _dataTypeService.GetDataType(id);
-                var configuration = dataType.ConfigurationAs<SliderConfiguration>();
+                var configuration = dataType?.ConfigurationAs<SliderConfiguration>();
                 return configuration?.EnableRange ?? false;
             });
         }
diff --git a/src/Umbraco.Core/PropertyEditors/ValueConverters/TagsValueConverter.cs b/src/Umbraco.Core/PropertyEditors/ValueConverters/TagsValueConverter.cs
index 2c45e5090a..da5dfd5416 100644
--- a/src/Umbraco.Core/PropertyEditors/ValueConverters/TagsValueConverter.cs
+++ b/src/Umbraco.Core/PropertyEditors/ValueConverters/TagsValueConverter.cs
@@ -67,7 +67,7 @@ namespace Umbraco.Cms.Core.PropertyEditors.ValueConverters
 
             return Storages.GetOrAdd(dataTypeId, id =>
             {
-                var configuration = _dataTypeService.GetDataType(id).ConfigurationAs<TagConfiguration>();
+                var configuration = _dataTypeService.GetDataType(id)?.ConfigurationAs<TagConfiguration>();
                 return configuration?.StorageType == TagsStorageType.Json;
             });
         }
diff --git a/src/Umbraco.Core/PublishedCache/IPublishedSnapshot.cs b/src/Umbraco.Core/PublishedCache/IPublishedSnapshot.cs
index 9ea08d36d0..3c55b9d699 100644
--- a/src/Umbraco.Core/PublishedCache/IPublishedSnapshot.cs
+++ b/src/Umbraco.Core/PublishedCache/IPublishedSnapshot.cs
@@ -23,7 +23,7 @@ namespace Umbraco.Cms.Core.PublishedCache
         /// <summary>
         /// Gets the <see cref="IPublishedMemberCache"/>.
         /// </summary>
-        IPublishedMemberCache Members { get; }
+        IPublishedMemberCache? Members { get; }
 
         /// <summary>
         /// Gets the <see cref="IDomainCache"/>.
diff --git a/src/Umbraco.Core/PublishedCache/PublishedElement.cs b/src/Umbraco.Core/PublishedCache/PublishedElement.cs
index 1972e8a7f4..69e3d6a156 100644
--- a/src/Umbraco.Core/PublishedCache/PublishedElement.cs
+++ b/src/Umbraco.Core/PublishedCache/PublishedElement.cs
@@ -46,7 +46,7 @@ namespace Umbraco.Cms.Core.PublishedCache
         // + using an initial reference cache level of .None ensures that everything will be
         // cached at .Content level - and that reference cache level will propagate to all
         // properties
-        public PublishedElement(IPublishedContentType contentType, Guid key, Dictionary<string, object> values, bool previewing)
+        public PublishedElement(IPublishedContentType contentType, Guid key, Dictionary<string, object?> values, bool previewing)
             : this(contentType, key, values, previewing, PropertyCacheLevel.None, null)
         { }
 
diff --git a/src/Umbraco.Core/Services/ConsentService.cs b/src/Umbraco.Core/Services/ConsentService.cs
index 5027df687b..bb4d989676 100644
--- a/src/Umbraco.Core/Services/ConsentService.cs
+++ b/src/Umbraco.Core/Services/ConsentService.cs
@@ -57,7 +57,7 @@ namespace Umbraco.Cms.Core.Services
         }
 
         /// <inheritdoc />
-        public IEnumerable<IConsent> LookupConsent(string? source = null, string? context = null, string? action = null,
+        public IEnumerable<IConsent>? LookupConsent(string? source = null, string? context = null, string? action = null,
             bool sourceStartsWith = false, bool contextStartsWith = false, bool actionStartsWith = false,
             bool includeHistory = false)
         {
diff --git a/src/Umbraco.Core/Services/ContentService.cs b/src/Umbraco.Core/Services/ContentService.cs
index b8b4b9ed25..e48a4d2d60 100644
--- a/src/Umbraco.Core/Services/ContentService.cs
+++ b/src/Umbraco.Core/Services/ContentService.cs
@@ -78,7 +78,7 @@ namespace Umbraco.Cms.Core.Services
             IContent? content = GetById(id);
 
             // Get the version
-            IContent version = GetVersion(versionId);
+            IContent? version = GetVersion(versionId);
 
             // Good old null checks
             if (content == null || version == null || content.Trashed)
@@ -457,9 +457,7 @@ namespace Umbraco.Cms.Core.Services
             {
                 scope.ReadLock(Constants.Locks.ContentTree);
                 IEnumerable<IContent> items = _documentRepository.GetMany(idsA);
-
                 var index = items.ToDictionary(x => x.Id, x => x);
-
                 return idsA.Select(x => index.TryGetValue(x, out IContent? c) ? c : null).WhereNotNull();
             }
         }
@@ -515,7 +513,7 @@ namespace Umbraco.Cms.Core.Services
         /// <returns>
         ///     <see cref="IContent" />
         /// </returns>
-        public IEnumerable<IContent> GetByIds(IEnumerable<Guid> ids)
+        public IEnumerable<IContent>? GetByIds(IEnumerable<Guid> ids)
         {
             Guid[] idsA = ids.ToArray();
             if (idsA.Length == 0)
@@ -526,11 +524,16 @@ namespace Umbraco.Cms.Core.Services
             using (IScope scope = ScopeProvider.CreateScope(autoComplete: true))
             {
                 scope.ReadLock(Constants.Locks.ContentTree);
-                IEnumerable<IContent> items = _documentRepository.GetMany(idsA);
+                IEnumerable<IContent>? items = _documentRepository.GetMany(idsA);
 
-                var index = items.ToDictionary(x => x.Key, x => x);
+                if (items is not null)
+                {
+                    var index = items.ToDictionary(x => x.Key, x => x);
 
-                return idsA.Select(x => index.TryGetValue(x, out IContent? c) ? c : null).WhereNotNull();
+                    return idsA.Select(x => index.TryGetValue(x, out IContent? c) ? c : null).WhereNotNull();
+                }
+
+                return null;
             }
         }
 
@@ -565,7 +568,7 @@ namespace Umbraco.Cms.Core.Services
 
         /// <inheritdoc />
         public IEnumerable<IContent> GetPagedOfTypes(int[] contentTypeIds, long pageIndex, int pageSize,
-            out long totalRecords, IQuery<IContent> filter, Ordering? ordering = null)
+            out long totalRecords, IQuery<IContent>? filter, Ordering? ordering = null)
         {
             if (pageIndex < 0)
             {
@@ -597,7 +600,7 @@ namespace Umbraco.Cms.Core.Services
         /// <param name="level">The level to retrieve Content from</param>
         /// <returns>An Enumerable list of <see cref="IContent" /> objects</returns>
         /// <remarks>Contrary to most methods, this method filters out trashed content items.</remarks>
-        public IEnumerable<IContent> GetByLevel(int level)
+        public IEnumerable<IContent>? GetByLevel(int level)
         {
             using (IScope scope = ScopeProvider.CreateScope(autoComplete: true))
             {
@@ -612,7 +615,7 @@ namespace Umbraco.Cms.Core.Services
         /// </summary>
         /// <param name="versionId">Id of the version to retrieve</param>
         /// <returns>An <see cref="IContent" /> item</returns>
-        public IContent GetVersion(int versionId)
+        public IContent? GetVersion(int versionId)
         {
             using (IScope scope = ScopeProvider.CreateScope(autoComplete: true))
             {
@@ -667,7 +670,7 @@ namespace Umbraco.Cms.Core.Services
         /// </summary>
         /// <param name="id">Id of the <see cref="IContent" /> to retrieve ancestors for</param>
         /// <returns>An Enumerable list of <see cref="IContent" /> objects</returns>
-        public IEnumerable<IContent> GetAncestors(int id)
+        public IEnumerable<IContent>? GetAncestors(int id)
         {
             // intentionally not locking
             IContent? content = GetById(id);
@@ -679,7 +682,7 @@ namespace Umbraco.Cms.Core.Services
         /// </summary>
         /// <param name="content"><see cref="IContent" /> to retrieve ancestors for</param>
         /// <returns>An Enumerable list of <see cref="IContent" /> objects</returns>
-        public IEnumerable<IContent> GetAncestors(IContent? content)
+        public IEnumerable<IContent>? GetAncestors(IContent? content)
         {
             //null check otherwise we get exceptions
             if (content?.Path.IsNullOrWhiteSpace() ?? true)
@@ -705,13 +708,13 @@ namespace Umbraco.Cms.Core.Services
         /// </summary>
         /// <param name="id">Id of the Parent to retrieve Children from</param>
         /// <returns>An Enumerable list of published <see cref="IContent" /> objects</returns>
-        public IEnumerable<IContent> GetPublishedChildren(int id)
+        public IEnumerable<IContent>? GetPublishedChildren(int id)
         {
             using (IScope scope = ScopeProvider.CreateScope(autoComplete: true))
             {
                 scope.ReadLock(Constants.Locks.ContentTree);
                 IQuery<IContent> query = Query<IContent>().Where(x => x.ParentId == id && x.Published);
-                return _documentRepository.Get(query).OrderBy(x => x.SortOrder);
+                return _documentRepository.Get(query)?.OrderBy(x => x.SortOrder);
             }
         }
 
@@ -827,7 +830,8 @@ namespace Umbraco.Cms.Core.Services
         /// <returns>Parent <see cref="IContent" /> object</returns>
         public IContent? GetParent(IContent? content)
         {
-            if (content?.ParentId == Constants.System.Root || content?.ParentId == Constants.System.RecycleBinContent || content is null)
+            if (content?.ParentId == Constants.System.Root || content?.ParentId == Constants.System.RecycleBinContent ||
+                content is null)
             {
                 return null;
             }
@@ -839,7 +843,7 @@ namespace Umbraco.Cms.Core.Services
         ///     Gets a collection of <see cref="IContent" /> objects, which reside at the first level / root
         /// </summary>
         /// <returns>An Enumerable list of <see cref="IContent" /> objects</returns>
-        public IEnumerable<IContent> GetRootContent()
+        public IEnumerable<IContent>? GetRootContent()
         {
             using (IScope scope = ScopeProvider.CreateScope(autoComplete: true))
             {
@@ -853,7 +857,7 @@ namespace Umbraco.Cms.Core.Services
         ///     Gets all published content items
         /// </summary>
         /// <returns></returns>
-        internal IEnumerable<IContent> GetAllPublished()
+        internal IEnumerable<IContent>? GetAllPublished()
         {
             using (IScope scope = ScopeProvider.CreateScope(autoComplete: true))
             {
@@ -947,7 +951,8 @@ namespace Umbraco.Cms.Core.Services
         #region Save, Publish, Unpublish
 
         /// <inheritdoc />
-        public OperationResult Save(IContent content, int userId = Constants.Security.SuperUserId, ContentScheduleCollection? contentSchedule = null)
+        public OperationResult Save(IContent content, int userId = Constants.Security.SuperUserId,
+            ContentScheduleCollection? contentSchedule = null)
         {
             PublishedState publishedState = content.PublishedState;
             if (publishedState != PublishedState.Published && publishedState != PublishedState.Unpublished)
@@ -1010,10 +1015,14 @@ namespace Umbraco.Cms.Core.Services
 
                 if (culturesChanging != null)
                 {
-                    var langs = string.Join(", ", _languageRepository.GetMany()
+                    var languages = _languageRepository.GetMany()?
                         .Where(x => culturesChanging.InvariantContains(x.IsoCode))
-                        .Select(x => x.CultureName));
-                    Audit(AuditType.SaveVariant, userId, content.Id, $"Saved languages: {langs}", langs);
+                        .Select(x => x.CultureName);
+                    if (languages is not null)
+                    {
+                        var langs = string.Join(", ", languages);
+                        Audit(AuditType.SaveVariant, userId, content.Id, $"Saved languages: {langs}", langs);
+                    }
                 }
                 else
                 {
@@ -1808,7 +1817,7 @@ namespace Umbraco.Cms.Core.Services
                             contentSchedule.Clear(culture, ContentScheduleAction.Release, date);
 
                             if (d.Trashed)
-                               {
+                            {
                                 continue; // won't publish
                             }
 
@@ -1827,7 +1836,7 @@ namespace Umbraco.Cms.Core.Services
 
                             publishing &= tryPublish; //set the culture to be published
                             if (!publishing)
-                               {
+                            {
                                 continue;
                             }
                         }
@@ -1993,7 +2002,7 @@ namespace Umbraco.Cms.Core.Services
 
                 // if not published, publish if force/root else do nothing
                 return force || isRoot
-                    ? new HashSet<string> { "*" } // "*" means 'publish all'
+                    ? new HashSet<string> {"*"} // "*" means 'publish all'
                     : null; // null means 'nothing to do'
             }
 
@@ -2321,8 +2330,8 @@ namespace Umbraco.Cms.Core.Services
 
                 if (deletePriorVersions)
                 {
-                    IContent content = GetVersion(versionId);
-                    DeleteVersions(id, content.UpdateDate, userId);
+                    IContent? content = GetVersion(versionId);
+                    DeleteVersions(id, content?.UpdateDate ?? DateTime.Now, userId);
                 }
 
                 scope.WriteLock(Constants.Locks.ContentTree);
@@ -2549,7 +2558,7 @@ namespace Umbraco.Cms.Core.Services
 
                 // emptying the recycle bin means deleting whatever is in there - do it properly!
                 IQuery<IContent> query = Query<IContent>().Where(x => x.ParentId == Constants.System.RecycleBinContent);
-                IContent[] contents = _documentRepository.Get(query).ToArray();
+                IContent[]? contents = _documentRepository.Get(query)?.ToArray();
 
                 var emptyingRecycleBinNotification = new ContentEmptyingRecycleBinNotification(contents, eventMessages);
                 if (scope.Notifications.PublishCancelable(emptyingRecycleBinNotification))
@@ -2558,10 +2567,13 @@ namespace Umbraco.Cms.Core.Services
                     return OperationResult.Cancel(eventMessages);
                 }
 
-                foreach (IContent content in contents)
+                if (contents is not null)
                 {
-                    DeleteLocked(scope, content, eventMessages);
-                    deleted.Add(content);
+                    foreach (IContent content in contents)
+                    {
+                        DeleteLocked(scope, content, eventMessages);
+                        deleted.Add(content);
+                    }
                 }
 
                 scope.Notifications.Publish(
@@ -2665,7 +2677,7 @@ namespace Umbraco.Cms.Core.Services
 
                 // keep track of copies
                 copies.Add(Tuple.Create(content, copy));
-                var idmap = new Dictionary<int, int> { [content.Id] = copy.Id };
+                var idmap = new Dictionary<int, int> {[content.Id] = copy.Id};
 
                 if (recursive) // process descendants
                 {
@@ -2965,19 +2977,22 @@ namespace Umbraco.Cms.Core.Services
             var pathMatch = content.Path + ",";
             IQuery<IContent> query = Query<IContent>()
                 .Where(x => x.Id != content.Id && x.Path.StartsWith(pathMatch) /*&& x.Trashed == false*/);
-            IEnumerable<IContent> contents = _documentRepository.Get(query);
+            IEnumerable<IContent>? contents = _documentRepository.Get(query);
 
             // beware! contents contains all published version below content
             // including those that are not directly published because below an unpublished content
             // these must be filtered out here
 
-            var parents = new List<int> { content.Id };
-            foreach (IContent c in contents)
+            var parents = new List<int> {content.Id};
+            if (contents is not null)
             {
-                if (parents.Contains(c.ParentId))
+                foreach (IContent c in contents)
                 {
-                    yield return c;
-                    parents.Add(c.Id);
+                    if (parents.Contains(c.ParentId))
+                    {
+                        yield return c;
+                        parents.Add(c.Id);
+                    }
                 }
             }
         }
@@ -2986,12 +3001,13 @@ namespace Umbraco.Cms.Core.Services
 
         #region Private Methods
 
-        private void Audit(AuditType type, int userId, int objectId, string? message = null, string? parameters = null) =>
+        private void Audit(AuditType type, int userId, int objectId, string? message = null,
+            string? parameters = null) =>
             _auditRepository.Save(new AuditItem(objectId, type, userId, UmbracoObjectTypes.Document.GetName(), message,
                 parameters));
 
-        private bool IsDefaultCulture(IReadOnlyCollection<ILanguage> langs, string culture) =>
-            langs.Any(x => x.IsDefault && x.IsoCode.InvariantEquals(culture));
+        private bool IsDefaultCulture(IReadOnlyCollection<ILanguage>? langs, string culture) =>
+            langs?.Any(x => x.IsDefault && x.IsoCode.InvariantEquals(culture)) ?? false;
 
         private bool IsMandatoryCulture(IReadOnlyCollection<ILanguage> langs, string culture) =>
             langs.Any(x => x.IsMandatory && x.IsoCode.InvariantEquals(culture));
@@ -3029,7 +3045,7 @@ namespace Umbraco.Cms.Core.Services
             var variesByCulture = content.ContentType.VariesByCulture();
 
             CultureImpact[] impactsToPublish = culturesPublishing == null
-                ? new[] { CultureImpact.Invariant } //if it's null it's invariant
+                ? new[] {CultureImpact.Invariant} //if it's null it's invariant
                 : culturesPublishing.Select(x =>
                     CultureImpact.Explicit(x,
                         allLangs.Any(lang => lang.IsoCode.InvariantEquals(x) && lang.IsMandatory))).ToArray();
@@ -3096,7 +3112,7 @@ namespace Umbraco.Cms.Core.Services
 
             ContentScheduleCollection contentSchedule = _documentRepository.GetContentSchedule(content.Id);
             //loop over each culture publishing - or string.Empty for invariant
-            foreach (var culture in culturesPublishing ?? new[] { string.Empty })
+            foreach (var culture in culturesPublishing ?? new[] {string.Empty})
             {
                 // ensure that the document status is correct
                 // note: culture will be string.Empty for invariant
@@ -3334,7 +3350,12 @@ namespace Umbraco.Cms.Core.Services
                 scope.WriteLock(Constants.Locks.ContentTree);
 
                 IQuery<IContent> query = Query<IContent>().WhereIn(x => x.ContentTypeId, contentTypeIdsA);
-                IContent[] contents = _documentRepository.Get(query).ToArray();
+                IContent[]? contents = _documentRepository.Get(query)?.ToArray();
+
+                if (contents is null)
+                {
+                    return;
+                }
 
                 if (scope.Notifications.PublishCancelable(new ContentDeletingNotification(contents, eventMessages)))
                 {
@@ -3357,12 +3378,15 @@ namespace Umbraco.Cms.Core.Services
                     // if current content has children, move them to trash
                     IContent c = content;
                     IQuery<IContent> childQuery = Query<IContent>().Where(x => x.ParentId == c.Id);
-                    IEnumerable<IContent> children = _documentRepository.Get(childQuery);
-                    foreach (IContent child in children)
+                    IEnumerable<IContent>? children = _documentRepository.Get(childQuery);
+                    if (children is not null)
                     {
-                        // see MoveToRecycleBin
-                        PerformMoveLocked(child, Constants.System.RecycleBinContent, null, userId, moves, true);
-                        changes.Add(new TreeChange<IContent>(content, TreeChangeTypes.RefreshBranch));
+                        foreach (IContent child in children)
+                        {
+                            // see MoveToRecycleBin
+                            PerformMoveLocked(child, Constants.System.RecycleBinContent, null, userId, moves, true);
+                            changes.Add(new TreeChange<IContent>(content, TreeChangeTypes.RefreshBranch));
+                        }
                     }
 
                     // delete content
@@ -3395,7 +3419,7 @@ namespace Umbraco.Cms.Core.Services
         /// <param name="contentTypeId">Id of the <see cref="IContentType" /></param>
         /// <param name="userId">Optional id of the user deleting the media</param>
         public void DeleteOfType(int contentTypeId, int userId = Constants.Security.SuperUserId) =>
-            DeleteOfTypes(new[] { contentTypeId }, userId);
+            DeleteOfTypes(new[] {contentTypeId}, userId);
 
         private IContentType GetContentType(IScope scope, string contentTypeAlias)
         {
@@ -3413,7 +3437,7 @@ namespace Umbraco.Cms.Core.Services
             scope.ReadLock(Constants.Locks.ContentTypes);
 
             IQuery<IContentType> query = Query<IContentType>().Where(x => x.Alias == contentTypeAlias);
-            IContentType? contentType = _contentTypeRepository.Get(query).FirstOrDefault();
+            IContentType? contentType = _contentTypeRepository.Get(query)?.FirstOrDefault();
 
             if (contentType == null)
             {
@@ -3524,7 +3548,7 @@ namespace Umbraco.Cms.Core.Services
             }
         }
 
-        private static readonly string?[] ArrayOfOneNullString = { null };
+        private static readonly string?[] ArrayOfOneNullString = {null};
 
         public IContent CreateContentFromBlueprint(IContent blueprint, string name,
             int userId = Constants.Security.SuperUserId)
@@ -3575,7 +3599,7 @@ namespace Umbraco.Cms.Core.Services
             return content;
         }
 
-        public IEnumerable<IContent> GetBlueprintsForContentTypes(params int[] contentTypeId)
+        public IEnumerable<IContent>? GetBlueprintsForContentTypes(params int[] contentTypeId)
         {
             using (ScopeProvider.CreateScope(autoComplete: true))
             {
@@ -3585,7 +3609,7 @@ namespace Umbraco.Cms.Core.Services
                     query.Where(x => contentTypeId.Contains(x.ContentTypeId));
                 }
 
-                return _documentBlueprintRepository.Get(query).Select(x =>
+                return _documentBlueprintRepository.Get(query)?.Select(x =>
                 {
                     x.Blueprint = true;
                     return x;
@@ -3609,24 +3633,27 @@ namespace Umbraco.Cms.Core.Services
                     query.Where(x => contentTypeIdsA.Contains(x.ContentTypeId));
                 }
 
-                IContent[] blueprints = _documentBlueprintRepository.Get(query).Select(x =>
+                IContent[]? blueprints = _documentBlueprintRepository.Get(query)?.Select(x =>
                 {
                     x.Blueprint = true;
                     return x;
                 }).ToArray();
 
-                foreach (IContent blueprint in blueprints)
+                if (blueprints is not null)
                 {
-                    _documentBlueprintRepository.Delete(blueprint);
-                }
+                    foreach (IContent blueprint in blueprints)
+                    {
+                        _documentBlueprintRepository.Delete(blueprint);
+                    }
 
-                scope.Notifications.Publish(new ContentDeletedBlueprintNotification(blueprints, evtMsgs));
-                scope.Complete();
+                    scope.Notifications.Publish(new ContentDeletedBlueprintNotification(blueprints, evtMsgs));
+                    scope.Complete();
+                }
             }
         }
 
         public void DeleteBlueprintsOfType(int contentTypeId, int userId = Constants.Security.SuperUserId) =>
-            DeleteBlueprintsOfTypes(new[] { contentTypeId }, userId);
+            DeleteBlueprintsOfTypes(new[] {contentTypeId}, userId);
 
         #endregion
     }
diff --git a/src/Umbraco.Core/Services/ContentServiceExtensions.cs b/src/Umbraco.Core/Services/ContentServiceExtensions.cs
index 1b9d9498f7..b3cb16e5f5 100644
--- a/src/Umbraco.Core/Services/ContentServiceExtensions.cs
+++ b/src/Umbraco.Core/Services/ContentServiceExtensions.cs
@@ -57,7 +57,7 @@ namespace Umbraco.Extensions
         }
         #endregion
 
-        public static IEnumerable<IContent> GetByIds(this IContentService contentService, IEnumerable<Udi> ids)
+        public static IEnumerable<IContent>? GetByIds(this IContentService contentService, IEnumerable<Udi> ids)
         {
             var guids = new List<GuidUdi>();
             foreach (var udi in ids)
diff --git a/src/Umbraco.Core/Services/ContentVersionService.cs b/src/Umbraco.Core/Services/ContentVersionService.cs
index d2b50cc82a..aa278324eb 100644
--- a/src/Umbraco.Core/Services/ContentVersionService.cs
+++ b/src/Umbraco.Core/Services/ContentVersionService.cs
@@ -80,8 +80,12 @@ namespace Umbraco.Cms.Core.Services
              */
             using (IScope scope = _scopeProvider.CreateScope(autoComplete: true))
             {
-                IReadOnlyCollection<ContentVersionMeta> allHistoricVersions = _documentVersionRepository.GetDocumentVersionsEligibleForCleanup();
+                IReadOnlyCollection<ContentVersionMeta>? allHistoricVersions = _documentVersionRepository.GetDocumentVersionsEligibleForCleanup();
 
+                if (allHistoricVersions is null)
+                {
+                    return Array.Empty<ContentVersionMeta>();
+                }
                 _logger.LogDebug("Discovered {count} candidate(s) for ContentVersion cleanup", allHistoricVersions.Count);
                 versionsToDelete = new List<ContentVersionMeta>(allHistoricVersions.Count);
 
@@ -135,7 +139,7 @@ namespace Umbraco.Cms.Core.Services
         }
 
         /// <inheritdoc />
-        public IEnumerable<ContentVersionMeta> GetPagedContentVersions(int contentId, long pageIndex, int pageSize, out long totalRecords, string? culture = null)
+        public IEnumerable<ContentVersionMeta>? GetPagedContentVersions(int contentId, long pageIndex, int pageSize, out long totalRecords, string? culture = null)
         {
             if (pageIndex < 0)
             {
@@ -163,7 +167,12 @@ namespace Umbraco.Cms.Core.Services
                 scope.WriteLock(Constants.Locks.ContentTree);
                 _documentVersionRepository.SetPreventCleanup(versionId, preventCleanup);
 
-                ContentVersionMeta version = _documentVersionRepository.Get(versionId);
+                ContentVersionMeta? version = _documentVersionRepository.Get(versionId);
+
+                if (version is null)
+                {
+                    return;
+                }
 
                 AuditType auditType = preventCleanup
                     ? AuditType.ContentVersionPreventCleanup
diff --git a/src/Umbraco.Core/Services/EntityService.cs b/src/Umbraco.Core/Services/EntityService.cs
index b971019be6..69f705ffee 100644
--- a/src/Umbraco.Core/Services/EntityService.cs
+++ b/src/Umbraco.Core/Services/EntityService.cs
@@ -55,7 +55,7 @@ namespace Umbraco.Cms.Core.Services
         }
 
         /// <inheritdoc />
-        public IEntitySlim Get(int id)
+        public IEntitySlim? Get(int id)
         {
             using (ScopeProvider.CreateScope(autoComplete: true))
             {
@@ -64,7 +64,7 @@ namespace Umbraco.Cms.Core.Services
         }
 
         /// <inheritdoc />
-        public IEntitySlim Get(Guid key)
+        public IEntitySlim? Get(Guid key)
         {
             using (ScopeProvider.CreateScope(autoComplete: true))
             {
@@ -73,7 +73,7 @@ namespace Umbraco.Cms.Core.Services
         }
 
         /// <inheritdoc />
-        public virtual IEntitySlim Get(int id, UmbracoObjectTypes objectType)
+        public virtual IEntitySlim? Get(int id, UmbracoObjectTypes objectType)
         {
             using (ScopeProvider.CreateScope(autoComplete: true))
             {
@@ -82,7 +82,7 @@ namespace Umbraco.Cms.Core.Services
         }
 
         /// <inheritdoc />
-        public IEntitySlim Get(Guid key, UmbracoObjectTypes objectType)
+        public IEntitySlim? Get(Guid key, UmbracoObjectTypes objectType)
         {
             using (ScopeProvider.CreateScope(autoComplete: true))
             {
@@ -91,7 +91,7 @@ namespace Umbraco.Cms.Core.Services
         }
 
         /// <inheritdoc />
-        public virtual IEntitySlim Get<T>(int id)
+        public virtual IEntitySlim? Get<T>(int id)
             where T : IUmbracoEntity
         {
             using (ScopeProvider.CreateScope(autoComplete: true))
@@ -101,7 +101,7 @@ namespace Umbraco.Cms.Core.Services
         }
 
         /// <inheritdoc />
-        public virtual IEntitySlim Get<T>(Guid key)
+        public virtual IEntitySlim? Get<T>(Guid key)
             where T : IUmbracoEntity
         {
             using (ScopeProvider.CreateScope(autoComplete: true))
@@ -235,7 +235,7 @@ namespace Umbraco.Cms.Core.Services
             using (ScopeProvider.CreateScope(autoComplete: true))
             {
                 var entity = _entityRepository.Get(id);
-                if (entity.ParentId == -1 || entity.ParentId == -20 || entity.ParentId == -21)
+                if (entity is null || entity.ParentId == -1 || entity.ParentId == -20 || entity.ParentId == -21)
                     return null;
                 return _entityRepository.Get(entity.ParentId);
             }
@@ -247,7 +247,7 @@ namespace Umbraco.Cms.Core.Services
             using (ScopeProvider.CreateScope(autoComplete: true))
             {
                 var entity = _entityRepository.Get(id);
-                if (entity.ParentId == -1 || entity.ParentId == -20 || entity.ParentId == -21)
+                if (entity is null || entity.ParentId == -1 || entity.ParentId == -20 || entity.ParentId == -21)
                     return null;
                 return _entityRepository.Get(entity.ParentId, objectType.GetGuid());
             }
@@ -279,7 +279,7 @@ namespace Umbraco.Cms.Core.Services
             using (ScopeProvider.CreateScope(autoComplete: true))
             {
                 var entity = _entityRepository.Get(id);
-                var pathMatch = entity.Path + ",";
+                var pathMatch = entity?.Path + ",";
                 var query = Query<IUmbracoEntity>().Where(x => x.Path.StartsWith(pathMatch) && x.Id != id);
                 return _entityRepository.GetByQuery(query);
             }
@@ -291,6 +291,10 @@ namespace Umbraco.Cms.Core.Services
             using (ScopeProvider.CreateScope(autoComplete: true))
             {
                 var entity = _entityRepository.Get(id);
+                if (entity is null)
+                {
+                    return Enumerable.Empty<IEntitySlim>();
+                }
                 var query = Query<IUmbracoEntity>().Where(x => x.Path.StartsWith(entity.Path) && x.Id != id);
                 return _entityRepository.GetByQuery(query, objectType.GetGuid());
             }
diff --git a/src/Umbraco.Core/Services/ExternalLoginService.cs b/src/Umbraco.Core/Services/ExternalLoginService.cs
index 291464f16f..1e8d25b8e8 100644
--- a/src/Umbraco.Core/Services/ExternalLoginService.cs
+++ b/src/Umbraco.Core/Services/ExternalLoginService.cs
@@ -33,12 +33,12 @@ namespace Umbraco.Cms.Core.Services
 
         /// <inheritdoc />
         [Obsolete("Use overload that takes a user/member key (Guid).")]
-        public IEnumerable<IIdentityUserLogin> GetExternalLogins(int userId)
+        public IEnumerable<IIdentityUserLogin>? GetExternalLogins(int userId)
             => GetExternalLogins(userId.ToGuid());
 
         /// <inheritdoc />
         [Obsolete("Use overload that takes a user/member key (Guid).")]
-        public IEnumerable<IIdentityUserToken> GetExternalLoginTokens(int userId) =>
+        public IEnumerable<IIdentityUserToken>? GetExternalLoginTokens(int userId) =>
             GetExternalLoginTokens(userId.ToGuid());
 
         /// <inheritdoc />
@@ -57,32 +57,32 @@ namespace Umbraco.Cms.Core.Services
             => DeleteUserLogins(userId.ToGuid());
 
         /// <inheritdoc />
-        public IEnumerable<IIdentityUserLogin> GetExternalLogins(Guid userOrMemberKey)
+        public IEnumerable<IIdentityUserLogin>? GetExternalLogins(Guid userOrMemberKey)
         {
             using (var scope = ScopeProvider.CreateScope(autoComplete: true))
             {
-                return _externalLoginRepository.Get(Query<IIdentityUserLogin>().Where(x => x.Key == userOrMemberKey))
+                return _externalLoginRepository.Get(Query<IIdentityUserLogin>().Where(x => x.Key == userOrMemberKey))?
                     .ToList();
             }
         }
 
         /// <inheritdoc />
-        public IEnumerable<IIdentityUserToken> GetExternalLoginTokens(Guid userOrMemberKey)
+        public IEnumerable<IIdentityUserToken>? GetExternalLoginTokens(Guid userOrMemberKey)
         {
             using (var scope = ScopeProvider.CreateScope(autoComplete: true))
             {
-                return _externalLoginRepository.Get(Query<IIdentityUserToken>().Where(x => x.Key == userOrMemberKey))
+                return _externalLoginRepository.Get(Query<IIdentityUserToken>().Where(x => x.Key == userOrMemberKey))?
                     .ToList();
             }
         }
 
         /// <inheritdoc />
-        public IEnumerable<IIdentityUserLogin> Find(string loginProvider, string providerKey)
+        public IEnumerable<IIdentityUserLogin>? Find(string loginProvider, string providerKey)
         {
             using (var scope = ScopeProvider.CreateScope(autoComplete: true))
             {
                 return _externalLoginRepository.Get(Query<IIdentityUserLogin>()
-                    .Where(x => x.ProviderKey == providerKey && x.LoginProvider == loginProvider))
+                    .Where(x => x.ProviderKey == providerKey && x.LoginProvider == loginProvider))?
                     .ToList();
             }
         }
diff --git a/src/Umbraco.Core/Services/IConsentService.cs b/src/Umbraco.Core/Services/IConsentService.cs
index 1833090501..50222a7f28 100644
--- a/src/Umbraco.Core/Services/IConsentService.cs
+++ b/src/Umbraco.Core/Services/IConsentService.cs
@@ -38,7 +38,7 @@ namespace Umbraco.Cms.Core.Services
         /// <param name="actionStartsWith">Determines whether <paramref name="action"/> is a start pattern.</param>
         /// <param name="includeHistory">Determines whether to include the history of consents.</param>
         /// <returns>Consents matching the parameters.</returns>
-        IEnumerable<IConsent> LookupConsent(string? source = null, string? context = null, string? action = null,
+        IEnumerable<IConsent>? LookupConsent(string? source = null, string? context = null, string? action = null,
             bool sourceStartsWith = false, bool contextStartsWith = false, bool actionStartsWith = false,
             bool includeHistory = false);
     }
diff --git a/src/Umbraco.Core/Services/IContentService.cs b/src/Umbraco.Core/Services/IContentService.cs
index 35fdb1f4d9..e53f091c49 100644
--- a/src/Umbraco.Core/Services/IContentService.cs
+++ b/src/Umbraco.Core/Services/IContentService.cs
@@ -26,7 +26,7 @@ namespace Umbraco.Cms.Core.Services
         /// <summary>
         /// Gets blueprints for a content type.
         /// </summary>
-        IEnumerable<IContent> GetBlueprintsForContentTypes(params int[] documentTypeId);
+        IEnumerable<IContent>? GetBlueprintsForContentTypes(params int[] documentTypeId);
 
         /// <summary>
         /// Saves a blueprint.
@@ -84,17 +84,17 @@ namespace Umbraco.Cms.Core.Services
         /// <summary>
         /// Gets documents.
         /// </summary>
-        IEnumerable<IContent> GetByIds(IEnumerable<int> ids);
+        IEnumerable<IContent>? GetByIds(IEnumerable<int> ids);
 
         /// <summary>
         /// Gets documents.
         /// </summary>
-        IEnumerable<IContent> GetByIds(IEnumerable<Guid> ids);
+        IEnumerable<IContent>? GetByIds(IEnumerable<Guid> ids);
 
         /// <summary>
         /// Gets documents at a given level.
         /// </summary>
-        IEnumerable<IContent> GetByLevel(int level);
+        IEnumerable<IContent>? GetByLevel(int level);
 
         /// <summary>
         /// Gets the parent of a document.
@@ -109,12 +109,12 @@ namespace Umbraco.Cms.Core.Services
         /// <summary>
         /// Gets ancestor documents of a document.
         /// </summary>
-        IEnumerable<IContent> GetAncestors(int id);
+        IEnumerable<IContent>? GetAncestors(int id);
 
         /// <summary>
         /// Gets ancestor documents of a document.
         /// </summary>
-        IEnumerable<IContent> GetAncestors(IContent content);
+        IEnumerable<IContent>? GetAncestors(IContent content);
 
         /// <summary>
         /// Gets all versions of a document.
@@ -137,12 +137,12 @@ namespace Umbraco.Cms.Core.Services
         /// <summary>
         /// Gets a version of a document.
         /// </summary>
-        IContent GetVersion(int versionId);
+        IContent? GetVersion(int versionId);
 
         /// <summary>
         /// Gets root-level documents.
         /// </summary>
-        IEnumerable<IContent> GetRootContent();
+        IEnumerable<IContent>? GetRootContent();
 
         /// <summary>
         /// Gets documents having an expiration date before (lower than, or equal to) a specified date.
diff --git a/src/Umbraco.Core/Services/IContentVersionService.cs b/src/Umbraco.Core/Services/IContentVersionService.cs
index 84b71213ff..d0f203b2ef 100644
--- a/src/Umbraco.Core/Services/IContentVersionService.cs
+++ b/src/Umbraco.Core/Services/IContentVersionService.cs
@@ -15,7 +15,7 @@ namespace Umbraco.Cms.Core.Services
         /// Gets paginated content versions for given content id paginated.
         /// </summary>
         /// <exception cref="ArgumentException">Thrown when <paramref name="culture"/> is invalid.</exception>
-        IEnumerable<ContentVersionMeta> GetPagedContentVersions(int contentId, long pageIndex, int pageSize, out long totalRecords, string? culture = null);
+        IEnumerable<ContentVersionMeta>? GetPagedContentVersions(int contentId, long pageIndex, int pageSize, out long totalRecords, string? culture = null);
 
         /// <summary>
         /// Updates preventCleanup value for given content version.
diff --git a/src/Umbraco.Core/Services/IEntityService.cs b/src/Umbraco.Core/Services/IEntityService.cs
index cb72735c02..66298aba1d 100644
--- a/src/Umbraco.Core/Services/IEntityService.cs
+++ b/src/Umbraco.Core/Services/IEntityService.cs
@@ -12,41 +12,41 @@ namespace Umbraco.Cms.Core.Services
         /// Gets an entity.
         /// </summary>
         /// <param name="id">The identifier of the entity.</param>
-        IEntitySlim Get(int id);
+        IEntitySlim? Get(int id);
 
         /// <summary>
         /// Gets an entity.
         /// </summary>
         /// <param name="key">The unique key of the entity.</param>
-        IEntitySlim Get(Guid key);
+        IEntitySlim? Get(Guid key);
 
         /// <summary>
         /// Gets an entity.
         /// </summary>
         /// <param name="id">The identifier of the entity.</param>
         /// <param name="objectType">The object type of the entity.</param>
-        IEntitySlim Get(int id, UmbracoObjectTypes objectType);
+        IEntitySlim? Get(int id, UmbracoObjectTypes objectType);
 
         /// <summary>
         /// Gets an entity.
         /// </summary>
         /// <param name="key">The unique key of the entity.</param>
         /// <param name="objectType">The object type of the entity.</param>
-        IEntitySlim Get(Guid key, UmbracoObjectTypes objectType);
+        IEntitySlim? Get(Guid key, UmbracoObjectTypes objectType);
 
         /// <summary>
         /// Gets an entity.
         /// </summary>
         /// <typeparam name="T">The type used to determine the object type of the entity.</typeparam>
         /// <param name="id">The identifier of the entity.</param>
-        IEntitySlim Get<T>(int id) where T : IUmbracoEntity;
+        IEntitySlim? Get<T>(int id) where T : IUmbracoEntity;
 
         /// <summary>
         /// Gets an entity.
         /// </summary>
         /// <typeparam name="T">The type used to determine the object type of the entity.</typeparam>
         /// <param name="key">The unique key of the entity.</param>
-        IEntitySlim Get<T>(Guid key) where T : IUmbracoEntity;
+        IEntitySlim? Get<T>(Guid key) where T : IUmbracoEntity;
 
         /// <summary>
         /// Determines whether an entity exists.
diff --git a/src/Umbraco.Core/Services/IExternalLoginService.cs b/src/Umbraco.Core/Services/IExternalLoginService.cs
index 75f8069f0c..05f131919e 100644
--- a/src/Umbraco.Core/Services/IExternalLoginService.cs
+++ b/src/Umbraco.Core/Services/IExternalLoginService.cs
@@ -15,14 +15,14 @@ namespace Umbraco.Cms.Core.Services
         /// </summary>
         /// <param name="userId"></param>
         /// <returns></returns>
-        IEnumerable<IIdentityUserLogin> GetExternalLogins(int userId);
+        IEnumerable<IIdentityUserLogin>? GetExternalLogins(int userId);
 
         /// <summary>
         /// Returns all user login tokens assigned
         /// </summary>
         /// <param name="userId"></param>
         /// <returns></returns>
-        IEnumerable<IIdentityUserToken> GetExternalLoginTokens(int userId);
+        IEnumerable<IIdentityUserToken>? GetExternalLoginTokens(int userId);
 
         /// <summary>
         /// Returns all logins matching the login info - generally there should only be one but in some cases
@@ -31,7 +31,7 @@ namespace Umbraco.Cms.Core.Services
         /// <param name="loginProvider"></param>
         /// <param name="providerKey"></param>
         /// <returns></returns>
-        IEnumerable<IIdentityUserLogin> Find(string loginProvider, string providerKey);
+        IEnumerable<IIdentityUserLogin>? Find(string loginProvider, string providerKey);
 
         /// <summary>
         /// Saves the external logins associated with the user
diff --git a/src/Umbraco.Core/Services/IExternalLoginWithKeyService.cs b/src/Umbraco.Core/Services/IExternalLoginWithKeyService.cs
index bc31f54f8b..1b378491c0 100644
--- a/src/Umbraco.Core/Services/IExternalLoginWithKeyService.cs
+++ b/src/Umbraco.Core/Services/IExternalLoginWithKeyService.cs
@@ -9,18 +9,18 @@ namespace Umbraco.Cms.Core.Services
         /// <summary>
         /// Returns all user logins assigned
         /// </summary>
-        IEnumerable<IIdentityUserLogin> GetExternalLogins(Guid userOrMemberKey);
+        IEnumerable<IIdentityUserLogin>? GetExternalLogins(Guid userOrMemberKey);
 
         /// <summary>
         /// Returns all user login tokens assigned
         /// </summary>
-        IEnumerable<IIdentityUserToken> GetExternalLoginTokens(Guid userOrMemberKey);
+        IEnumerable<IIdentityUserToken>? GetExternalLoginTokens(Guid userOrMemberKey);
 
         /// <summary>
         /// Returns all logins matching the login info - generally there should only be one but in some cases
         /// there might be more than one depending on if an administrator has been editing/removing members
         /// </summary>
-        IEnumerable<IIdentityUserLogin> Find(string loginProvider, string providerKey);
+        IEnumerable<IIdentityUserLogin>? Find(string loginProvider, string providerKey);
 
         /// <summary>
         /// Saves the external logins associated with the user
diff --git a/src/Umbraco.Core/Services/IMembershipMemberService.cs b/src/Umbraco.Core/Services/IMembershipMemberService.cs
index 48900752e2..f183882b55 100644
--- a/src/Umbraco.Core/Services/IMembershipMemberService.cs
+++ b/src/Umbraco.Core/Services/IMembershipMemberService.cs
@@ -99,7 +99,7 @@ namespace Umbraco.Cms.Core.Services
         /// <remarks>An <see cref="IMembershipUser"/> can be of type <see cref="IMember"/> or <see cref="IUser"/></remarks>
         /// <param name="username">Username to use for retrieval</param>
         /// <returns><see cref="IMembershipUser"/></returns>
-        T GetByUsername(string username);
+        T? GetByUsername(string username);
 
         /// <summary>
         /// Deletes an <see cref="IMembershipUser"/>
diff --git a/src/Umbraco.Core/Services/IUserService.cs b/src/Umbraco.Core/Services/IUserService.cs
index ee16ef64a6..3149ad0370 100644
--- a/src/Umbraco.Core/Services/IUserService.cs
+++ b/src/Umbraco.Core/Services/IUserService.cs
@@ -106,7 +106,7 @@ namespace Umbraco.Cms.Core.Services
         /// </summary>
         /// <param name="username">Username</param>
         /// <returns><see cref="IProfile"/></returns>
-        IProfile GetProfileByUserName(string username);
+        IProfile? GetProfileByUserName(string username);
 
         /// <summary>
         /// Gets a user by Id
diff --git a/src/Umbraco.Core/Services/PropertyValidationService.cs b/src/Umbraco.Core/Services/PropertyValidationService.cs
index 7aea02ca57..c5a4312776 100644
--- a/src/Umbraco.Core/Services/PropertyValidationService.cs
+++ b/src/Umbraco.Core/Services/PropertyValidationService.cs
@@ -31,7 +31,7 @@ namespace Umbraco.Cms.Core.Services
         /// <inheritdoc />
         public IEnumerable<ValidationResult> ValidatePropertyValue(
            IPropertyType propertyType,
-           object postedValue)
+           object? postedValue)
         {
             if (propertyType is null) throw new ArgumentNullException(nameof(propertyType));
             var dataType = _dataTypeService.GetDataType(propertyType.DataTypeId);
@@ -47,7 +47,7 @@ namespace Umbraco.Cms.Core.Services
         public IEnumerable<ValidationResult> ValidatePropertyValue(
             IDataEditor editor,
             IDataType dataType,
-            object postedValue,
+            object? postedValue,
             bool isRequired,
             string? validationRegExp,
             string? isRequiredMessage,
@@ -190,7 +190,7 @@ namespace Umbraco.Cms.Core.Services
                 // the property will be displayed as a label, so flagging it as invalid would be pointless.
                 return true;
             }
-            var configuration = _dataTypeService.GetDataType(propertyType.DataTypeId).Configuration;
+            var configuration = _dataTypeService.GetDataType(propertyType.DataTypeId)?.Configuration;
             var valueEditor = editor.GetValueEditor(configuration);
             return !valueEditor.Validate(value, propertyType.Mandatory, propertyType.ValidationRegExp).Any();
         }
diff --git a/src/Umbraco.Core/Services/UserService.cs b/src/Umbraco.Core/Services/UserService.cs
index d3b52701bc..a6bad5b2fe 100644
--- a/src/Umbraco.Core/Services/UserService.cs
+++ b/src/Umbraco.Core/Services/UserService.cs
@@ -183,7 +183,7 @@ namespace Umbraco.Cms.Core.Services
             using (var scope = ScopeProvider.CreateScope(autoComplete: true))
             {
                 var query = Query<IUser>().Where(x => x.Email.Equals(email));
-                return _userRepository.Get(query).FirstOrDefault();
+                return _userRepository.Get(query)?.FirstOrDefault();
             }
         }
 
@@ -192,7 +192,7 @@ namespace Umbraco.Cms.Core.Services
         /// </summary>
         /// <param name="username">Username to use for retrieval</param>
         /// <returns><see cref="IUser"/></returns>
-        public IUser GetByUsername(string username)
+        public IUser? GetByUsername(string username)
         {
             using (var scope = ScopeProvider.CreateScope(autoComplete: true))
             {
@@ -649,7 +649,7 @@ namespace Umbraco.Cms.Core.Services
         /// </summary>
         /// <param name="username">Username</param>
         /// <returns><see cref="IProfile"/></returns>
-        public IProfile GetProfileByUserName(string username)
+        public IProfile? GetProfileByUserName(string username)
         {
             using (var scope = ScopeProvider.CreateScope(autoComplete: true))
             {
@@ -770,7 +770,7 @@ namespace Umbraco.Cms.Core.Services
             {
                 var query = Query<IUserGroup>().Where(x => aliases.SqlIn(x.Alias));
                 var contents = _userGroupRepository.Get(query);
-                return contents.WhereNotNull().ToArray();
+                return contents?.WhereNotNull().ToArray() ?? Enumerable.Empty<IUserGroup>();
             }
         }
 
@@ -787,7 +787,7 @@ namespace Umbraco.Cms.Core.Services
             {
                 var query = Query<IUserGroup>().Where(x => x.Alias == alias);
                 var contents = _userGroupRepository.Get(query);
-                return contents.FirstOrDefault();
+                return contents?.FirstOrDefault();
             }
         }
 
diff --git a/src/Umbraco.Core/Sync/RefreshInstruction.cs b/src/Umbraco.Core/Sync/RefreshInstruction.cs
index 169b58f5a1..b8609410ab 100644
--- a/src/Umbraco.Core/Sync/RefreshInstruction.cs
+++ b/src/Umbraco.Core/Sync/RefreshInstruction.cs
@@ -106,12 +106,12 @@ namespace Umbraco.Cms.Core.Sync
                     if (idType == typeof(int))
                     {
                         // Bulk of ints is supported
-                        var intIds = ids.Cast<int>().ToArray();
-                        return new[] { new RefreshInstruction(refresher, RefreshMethodType.RefreshByIds, jsonSerializer.Serialize(intIds), intIds.Length) };
+                        var intIds = ids?.Cast<int>().ToArray();
+                        return new[] { new RefreshInstruction(refresher, RefreshMethodType.RefreshByIds, jsonSerializer.Serialize(intIds), intIds?.Length ?? 0) };
                     }
 
                     // Else must be guids, bulk of guids is not supported, so iterate.
-                    return ids.Select(x => new RefreshInstruction(refresher, RefreshMethodType.RefreshByGuid, (Guid) x));
+                    return ids?.Select(x => new RefreshInstruction(refresher, RefreshMethodType.RefreshByGuid, (Guid) x)) ?? Enumerable.Empty<RefreshInstruction>();
 
                 case MessageType.RemoveById:
                     if (idType == null)
@@ -120,7 +120,7 @@ namespace Umbraco.Cms.Core.Sync
                     }
 
                     // Must be ints, bulk-remove is not supported, so iterate.
-                    return ids.Select(x => new RefreshInstruction(refresher, RefreshMethodType.RemoveById, (int) x));
+                    return ids?.Select(x => new RefreshInstruction(refresher, RefreshMethodType.RemoveById, (int) x)) ?? Enumerable.Empty<RefreshInstruction>();
                     //return new[] { new RefreshInstruction(refresher, RefreshMethodType.RemoveByIds, JsonConvert.SerializeObject(ids.Cast<int>().ToArray())) };
 
                 default:
diff --git a/src/Umbraco.Core/Trees/TreeNode.cs b/src/Umbraco.Core/Trees/TreeNode.cs
index ccf5a38347..ba856b6d3a 100644
--- a/src/Umbraco.Core/Trees/TreeNode.cs
+++ b/src/Umbraco.Core/Trees/TreeNode.cs
@@ -38,7 +38,7 @@ namespace Umbraco.Cms.Core.Trees
         }
 
         [DataMember(Name = "parentId", IsRequired = true)]
-        public new object ParentId { get; set; }
+        public new object? ParentId { get; set; }
 
         /// <summary>
         /// A flag to set whether or not this node has children
diff --git a/src/Umbraco.Core/Udi.cs b/src/Umbraco.Core/Udi.cs
index 55efc549eb..c18bed7a90 100644
--- a/src/Umbraco.Core/Udi.cs
+++ b/src/Umbraco.Core/Udi.cs
@@ -157,7 +157,7 @@ namespace Umbraco.Cms.Core
         public static bool operator ==(Udi? udi1, Udi? udi2)
         {
             if (ReferenceEquals(udi1, udi2)) return true;
-            if ((object)udi1 == null || (object)udi2 == null) return false;
+            if ((object?)udi1 == null || (object?)udi2 == null) return false;
             return udi1.Equals(udi2);
         }
 
diff --git a/src/Umbraco.Core/Web/HybridUmbracoContextAccessor.cs b/src/Umbraco.Core/Web/HybridUmbracoContextAccessor.cs
index 033206a453..94710429f0 100644
--- a/src/Umbraco.Core/Web/HybridUmbracoContextAccessor.cs
+++ b/src/Umbraco.Core/Web/HybridUmbracoContextAccessor.cs
@@ -1,3 +1,4 @@
+using System.Diagnostics.CodeAnalysis;
 using Umbraco.Cms.Core.Cache;
 
 namespace Umbraco.Cms.Core.Web
@@ -17,7 +18,7 @@ namespace Umbraco.Cms.Core.Web
         /// <summary>
         /// Tries to get the <see cref="UmbracoContext"/> object.
         /// </summary>
-        public bool TryGetUmbracoContext(out IUmbracoContext? umbracoContext)
+        public bool TryGetUmbracoContext([MaybeNullWhen(false)] out IUmbracoContext umbracoContext)
         {
             umbracoContext = Value;
 
diff --git a/src/Umbraco.Infrastructure/Install/InstallSteps/DatabaseUpgradeStep.cs b/src/Umbraco.Infrastructure/Install/InstallSteps/DatabaseUpgradeStep.cs
index 693cd1cbde..c0e272a6aa 100644
--- a/src/Umbraco.Infrastructure/Install/InstallSteps/DatabaseUpgradeStep.cs
+++ b/src/Umbraco.Infrastructure/Install/InstallSteps/DatabaseUpgradeStep.cs
@@ -55,7 +55,7 @@ namespace Umbraco.Cms.Infrastructure.Install.InstallSteps
 
                 var result = _databaseBuilder.UpgradeSchemaAndData(plan);
 
-                if (result.Success == false)
+                if (result?.Success == false)
                 {
                     throw new InstallException("The database failed to upgrade. ERROR: " + result.Message);
                 }
diff --git a/tests/Umbraco.Tests.Integration/Umbraco.Web.BackOffice/Controllers/ContentControllerTests.cs b/tests/Umbraco.Tests.Integration/Umbraco.Web.BackOffice/Controllers/ContentControllerTests.cs
index b91e87907a..ec5968e92d 100644
--- a/tests/Umbraco.Tests.Integration/Umbraco.Web.BackOffice/Controllers/ContentControllerTests.cs
+++ b/tests/Umbraco.Tests.Integration/Umbraco.Web.BackOffice/Controllers/ContentControllerTests.cs
@@ -529,6 +529,7 @@ namespace Umbraco.Cms.Tests.Integration.Umbraco.Web.BackOffice.Controllers
 
             var url = PrepareApiControllerUrl<ContentController>(x => x.PostSave(null));
 
+            var result = JsonConvert.SerializeObject(model);
             HttpResponseMessage response = await Client.PostAsync(url, new MultipartFormDataContent
             {
                 { new StringContent(JsonConvert.SerializeObject(model)), "contentItem" }