Add so only controllers are left

src/Umbraco.Core/Security/ContentPermissions.cs

@@ -46,7 +46,7 @@ namespace Umbraco.Cms.Core.Security
             char permissionToCheck) => CheckPermissions(content, user, new[] { permissionToCheck });
 
         public ContentAccess CheckPermissions(
-            IContent content,
+            IContent? content,
             IUser? user,
             IReadOnlyList<char> permissionsToCheck)
         {

src/Umbraco.Web.BackOffice/DependencyInjection/UmbracoBuilderExtensions.cs

@@ -33,7 +33,7 @@ namespace Umbraco.Extensions
         /// <summary>
         /// Adds all required components to run the Umbraco back office
         /// </summary>
-        public static IUmbracoBuilder AddBackOffice(this IUmbracoBuilder builder, Action<IMvcBuilder> configureMvc = null) => builder
+        public static IUmbracoBuilder AddBackOffice(this IUmbracoBuilder builder, Action<IMvcBuilder>? configureMvc = null) => builder
                 .AddConfiguration()
                 .AddUmbracoCore()
                 .AddWebComponents()
@@ -77,7 +77,7 @@ namespace Umbraco.Extensions
         /// <summary>
         /// Gets the back office tree collection builder
         /// </summary>
-        public static TreeCollectionBuilder Trees(this IUmbracoBuilder builder)
+        public static TreeCollectionBuilder? Trees(this IUmbracoBuilder builder)
             => builder.WithCollectionBuilder<TreeCollectionBuilder>();
 
         public static IUmbracoBuilder AddBackOfficeCore(this IUmbracoBuilder builder)
@@ -97,7 +97,7 @@ namespace Umbraco.Extensions
             // the collection builder only accepts types inheriting from TreeControllerBase
             // and will filter out those that are not attributed with TreeAttribute
             var umbracoApiControllerTypes = builder.TypeLoader.GetUmbracoApiControllers().ToList();
-            builder.Trees()
+            builder.Trees()?
                 .AddTreeControllers(umbracoApiControllerTypes.Where(x => typeof(TreeControllerBase).IsAssignableFrom(x)));
 
             builder.AddWebMappingProfiles();