Fixed: Avoid lookups for empty MusicBrainz IDs in import list fetching

src/NzbDrone.Core/ImportLists/ImportListSyncService.cs

@@ -163,7 +163,7 @@ namespace NzbDrone.Core.ImportLists
 
         private void ProcessAlbumReport(ImportListDefinition importList, ImportListItemInfo report, Dictionary<string, ImportListExclusion> listExclusions, List<Album> albumsToAdd, List<Artist> artistsToAdd)
         {
-            if (report.AlbumMusicBrainzId == null || report.ArtistMusicBrainzId == null)
+            if (report.AlbumMusicBrainzId.IsNullOrWhiteSpace() || report.ArtistMusicBrainzId.IsNullOrWhiteSpace())
             {
                 return;
             }
@@ -267,7 +267,7 @@ namespace NzbDrone.Core.ImportLists
 
         private Artist ProcessArtistReport(ImportListDefinition importList, ImportListItemInfo report, Dictionary<string, ImportListExclusion> listExclusions, List<Artist> artistsToAdd)
         {
-            if (report.ArtistMusicBrainzId == null)
+            if (report.ArtistMusicBrainzId.IsNullOrWhiteSpace())
             {
                 return null;
             }

src/NzbDrone.Core/Music/Repositories/ArtistRepository.cs

@@ -47,11 +47,9 @@ namespace NzbDrone.Core.Music
 
         public Artist FindById(string foreignArtistId)
         {
-            Artist artist;
+            var artist = Query(Builder().Where<ArtistMetadata>(m => m.ForeignArtistId == foreignArtistId)).SingleOrDefault();
 
-            artist = Query(Builder().Where<ArtistMetadata>(m => m.ForeignArtistId == foreignArtistId)).SingleOrDefault();
-
-            if (artist == null)
+            if (artist == null && foreignArtistId.IsNotNullOrWhiteSpace())
             {
                 artist = Query(Builder().Where<ArtistMetadata>(x => x.OldForeignArtistIds.Contains(foreignArtistId))).SingleOrDefault();
             }