Fixed: Don't die in Collections when a collection doesn't have movies

src/Radarr.Api.V3/Collections/CollectionController.cs

@@ -159,6 +159,8 @@ namespace Radarr.Api.V3.Collections
 
                 allCollectionMovies.TryGetValue(collection.TmdbId, out var collectionMovies);
 
+                if (collectionMovies != null)
+                {
                     foreach (var movie in collectionMovies)
                     {
                         var translation = GetTranslationFromDict(tdict, movie, configLanguage);
@@ -173,6 +175,7 @@ namespace Radarr.Api.V3.Collections
 
                         resource.Movies.Add(movieResource);
                     }
+                }
 
                 yield return resource;
             }