Fixed: Custom script unable to execute when release processed via /release/push API

src/NzbDrone.Core/Notifications/CustomScript/CustomScript.cs

@@ -49,7 +49,7 @@ namespace NzbDrone.Core.Notifications.CustomScript
             environmentVariables.Add("Sonarr_Release_EpisodeAirDatesUtc", string.Join(",", remoteEpisode.Episodes.Select(e => e.AirDateUtc)));
             environmentVariables.Add("Sonarr_Release_EpisodeTitles", string.Join("|", remoteEpisode.Episodes.Select(e => e.Title)));
             environmentVariables.Add("Sonarr_Release_Title", remoteEpisode.Release.Title);
-            environmentVariables.Add("Sonarr_Release_Indexer", remoteEpisode.Release.Indexer);
+            environmentVariables.Add("Sonarr_Release_Indexer", remoteEpisode.Release.Indexer ?? string.Empty);
             environmentVariables.Add("Sonarr_Release_Size", remoteEpisode.Release.Size.ToString());
             environmentVariables.Add("Sonarr_Release_Quality", remoteEpisode.ParsedEpisodeInfo.Quality.Quality.Name);
             environmentVariables.Add("Sonarr_Release_QualityVersion", remoteEpisode.ParsedEpisodeInfo.Quality.Revision.Version.ToString());