def get_document_hash(self, doc_id: str) -> Optional[str]:
        """Get the stored hash for a document, if it exists."""
        metadata = self._kvstore.get(doc_id, collection=self._metadata_collection)
        if metadata is not None:
            return metadata.get("doc_hash", None)
        else:
            return None
Get the stored hash for a document, if it exists.
llama-index-core/llama_index/core/storage/docstore/keyval_docstore.py