Migration will clean unmapped history items

NzbDrone.Core/Datastore/Migrations/Migration20120727.cs

@@ -0,0 +1,25 @@
+using System;
+using System.Data;
+using Migrator.Framework;
+using NzbDrone.Common;
+
+namespace NzbDrone.Core.Datastore.Migrations
+{
+
+    [Migration(20120727)]
+    public class Migration20120727 : NzbDroneMigration
+    {
+        protected override void MainDbUpgrade()
+        {
+            Database.ExecuteNonQuery(@"DELETE FROM History
+                                        WHERE HistoryId IN
+                                        (
+                                            SELECT History.HistoryId
+                                            FROM History
+                                            LEFT OUTER JOIN Episodes
+                                            ON History.EpisodeId = Episodes.EpisodeId
+                                            WHERE Episodes.Title is null
+                                        )");
+            }
+    }
+}