Merge pull request #4643 from crobibero/empty-lib-null-ref

Fix null reference when getting filters of an empty library

Jellyfin.Api/Controllers/FilterController.cs

@@ -83,7 +83,12 @@ namespace Jellyfin.Api.Controllers
                 }
             };
 
-            var itemList = ((Folder)item!).GetItemList(query);
+            if (item is not Folder folder)
+            {
+                return new QueryFiltersLegacy();
+            }
+
+            var itemList = folder.GetItemList(query);
             return new QueryFiltersLegacy
             {
                 Years = itemList.Select(i => i.ProductionYear ?? -1)