Avoid None values [..., None, ...] in the snapshots key's value with list_versions. This may happen if during the runtime of list_version a new snapshot is created.

Author: dimosped

arctic/store/version_store.py

@@ -260,7 +260,7 @@ def list_versions(self, symbol=None, snapshot=None, latest_only=False):
                                  'deleted': meta.get('deleted', False) if meta else False,
                                  # We return offset-aware datetimes in Local Time.
                                  'date': ms_to_datetime(datetime_to_ms(version['_id'].generation_time)),
-                                 'snapshots': [snapshots.get(s) for s in version.get('parent', [])]})
+                                 'snapshots': [snapshots[s] for s in version.get('parent', []) if s in snapshots]})
         return versions
 
     def _find_snapshots(self, parent_ids):