adjusting syntax

Signed-off-by: Francisco Javier Arceo <[email protected]>

sdk/python/feast/feature_store.py

@@ -1881,7 +1881,7 @@ def retrieve_online_documents_v2(
             distance_metric: The distance metric to use for retrieval.
             query_string: The query string to retrieve the closest document features using keyword search (bm25).
         """
-        assert query or query_string, "Either query or query_string must be provided."
+        assert query is not None or query_string is not None, "Either query or query_string must be provided."
 
         (
             available_feature_views,