Fixed: Cleanup of unused tags for Import lists.

Fixes #4610

src/NzbDrone.Core/Housekeeping/Housekeepers/CleanupUnusedTags.cs

@@ -1,6 +1,7 @@
 using System.Collections.Generic;
 using System.Linq;
 using Marr.Data;
+using NzbDrone.Common.Extensions;
 using NzbDrone.Common.Serializer;
 using NzbDrone.Core.Datastore;
 
@@ -19,19 +20,19 @@ namespace NzbDrone.Core.Housekeeping.Housekeepers
         {
             var mapper = _database.GetDataMapper();
 
-            var usedTags = new[] { "Series", "Notifications", "DelayProfiles", "ReleaseProfiles" }
+            var usedTags = new[] { "Series", "Notifications", "DelayProfiles", "ReleaseProfiles", "ImportLists", "Indexers" }
                 .SelectMany(v => GetUsedTags(v, mapper))
                 .Distinct()
-                .ToArray();
+                .ToList();
 
-            var usedTagsList = string.Join(",", usedTags.Select(d => d.ToString()).ToArray());
+            var usedTagsList = usedTags.Select(d => d.ToString()).Join(",");
 
             mapper.ExecuteNonQuery($"DELETE FROM Tags WHERE NOT Id IN ({usedTagsList})");
         }
 
         private int[] GetUsedTags(string table, IDataMapper mapper)
         {
-            return mapper.ExecuteReader($"SELECT DISTINCT Tags FROM {table} WHERE NOT Tags = '[]'", reader => reader.GetString(0))
+            return mapper.ExecuteReader($"SELECT DISTINCT Tags FROM {table} WHERE NOT Tags = '[]' AND NOT Tags IS NULL", reader => reader.GetString(0))
                          .SelectMany(Json.Deserialize<List<int>>)
                          .Distinct()
                          .ToArray();