async def _aget_ref_doc_id(self, doc_id: str) -> Optional[str]:
        """Helper function to get ref_doc_info for a given doc_id."""
        metadata = await self._kvstore.aget(
            doc_id, collection=self._metadata_collection
        )
        if metadata is None:
            return None

        return metadata.get("ref_doc_id", None)
Helper function to get ref_doc_info for a given doc_id.
llama-index-core/llama_index/core/storage/docstore/keyval_docstore.py