feat: allowed to append none to source collection

music_kraken/objects/source.py

@@ -122,6 +122,9 @@ class SourceCollection:
             yield from self._page_to_source_list[page]
 
     def append(self, source: Source):
+        if source is None:
+            return
+
         existing_source = None
         for key in source.indexing_values:
             if key in self._indexed_sources: