Fixed: Creating root folders without default tags

Fixes #4898

src/Lidarr.Api.V1/RootFolders/RootFolderResource.cs

@@ -67,7 +67,7 @@ namespace Lidarr.Api.V1.RootFolders
                 DefaultQualityProfileId = resource.DefaultQualityProfileId,
                 DefaultMonitorOption = resource.DefaultMonitorOption,
                 DefaultNewItemMonitorOption = resource.DefaultNewItemMonitorOption,
-                DefaultTags = resource.DefaultTags,
+                DefaultTags = resource.DefaultTags ?? new HashSet<int>()
             };
         }
 

src/NzbDrone.Core/RootFolders/RootFolder.cs

@@ -12,7 +12,7 @@ namespace NzbDrone.Core.RootFolders
         public int DefaultQualityProfileId { get; set; }
         public MonitorTypes DefaultMonitorOption { get; set; }
         public NewItemMonitorTypes DefaultNewItemMonitorOption { get; set; }
-        public HashSet<int> DefaultTags { get; set; }
+        public HashSet<int> DefaultTags { get; set; } = new ();
 
         public bool Accessible { get; set; }
         public long? FreeSpace { get; set; }