V14: Fix null ref exception in current user permission endpoint (#16286)

* Fix null reference exception

* Align behaviour with document and media version

src/Umbraco.Cms.Api.Management/Controllers/User/UserOrCurrentUserControllerBase.cs

@@ -116,6 +116,10 @@ public abstract class UserOrCurrentUserControllerBase : ManagementApiControllerB
                 .WithTitle("Content node not found")
                 .WithDetail("The specified content node was not found.")
                 .Build()),
+            UserOperationStatus.NodeNotFound => NotFound(problemDetailsBuilder
+                .WithTitle("Node not found")
+                .WithDetail("The specified node was not found.")
+                .Build()),
             UserOperationStatus.NotInInviteState => BadRequest(problemDetailsBuilder
                 .WithTitle("Invalid user state")
                 .WithDetail("The target user is not in the invite state.")

src/Umbraco.Core/Services/OperationStatus/UserOperationStatus.cs

@@ -34,6 +34,7 @@ public enum UserOperationStatus
     MediaStartNodeNotFound,
     ContentNodeNotFound,
     MediaNodeNotFound,
+    NodeNotFound,
     UnknownFailure,
     CannotPasswordReset,
     NotInInviteState,

src/Umbraco.Core/Services/UserService.cs

@@ -13,6 +13,7 @@ using Umbraco.Cms.Core.Events;
 using Umbraco.Cms.Core.Exceptions;
 using Umbraco.Cms.Core.IO;
 using Umbraco.Cms.Core.Models;
+using Umbraco.Cms.Core.Models.Entities;
 using Umbraco.Cms.Core.Models.Membership;
 using Umbraco.Cms.Core.Models.TemporaryFile;
 using Umbraco.Cms.Core.Notifications;
@@ -2339,7 +2340,18 @@ internal class UserService : RepositoryService, IUserService
         }
 
         // We don't know what the entity type may be, so we have to get the entire entity :(
-        var idKeyMap = keys.ToDictionary(key => _entityService.Get(key)!.Id);
+        Dictionary<int, Guid> idKeyMap = new();
+        foreach (Guid key in keys)
+        {
+            IEntitySlim? entity = _entityService.Get(key);
+
+            if (entity is null)
+            {
+                return Attempt.FailWithStatus(UserOperationStatus.NodeNotFound, Enumerable.Empty<NodePermissions>());
+            }
+
+            idKeyMap[entity.Id] = key;
+        }
 
         EntityPermissionCollection permissionCollection = _userGroupRepository.GetPermissions(user.Groups.ToArray(), true, idKeyMap.Keys.ToArray());