support empty list

Author: jamesfisher-geo

stac_fastapi/elasticsearch/stac_fastapi/elasticsearch/database_logic.py

@@ -168,7 +168,7 @@ def indices(collection_ids: Optional[List[str]]) -> str:
     Returns:
         A string of comma-separated index names. If `collection_ids` is None, returns the default indices.
     """
-    if collection_ids is None:
+    if collection_ids is None or collection_ids == []:
         return ITEM_INDICES
     else:
         return ",".join([index_by_collection_id(c) for c in collection_ids])