Merge pull request #17395 from paoloantinori/fix/userdata-null-user-nre-master

Avoid NRE when sorting by user-dependent keys without a user

Emby.Server.Implementations/Library/LibraryManager.cs

@@ -2315,9 +2315,13 @@ namespace Emby.Server.Implementations.Library
         {
             var comparer = Comparers.FirstOrDefault(c => name == c.Type);
 
-            // If it requires a user, create a new one, and assign the user
             if (comparer is IUserBaseItemComparer)
             {
+                if (user is null)
+                {
+                    throw new ArgumentException($"Sort key '{name}' requires a user, but none was provided.");
+                }
+
                 var userComparer = (IUserBaseItemComparer)Activator.CreateInstance(comparer.GetType())!; // only null for Nullable<T> instances
 
                 userComparer.User = user;

Emby.Server.Implementations/Library/UserDataManager.cs

@@ -352,6 +352,7 @@ namespace Emby.Server.Implementations.Library
         /// <inheritdoc />
         public UserItemData? GetUserData(User user, BaseItem item)
         {
+            ArgumentNullException.ThrowIfNull(user);
             var row = ResolveUserDataRow(item, item.UserData?.Where(e => e.UserId.Equals(user.Id)));
             return row is not null ? Map(row) : new UserItemData()
             {