def _index_schema(self) -> Optional[dict]:
        """
        Return the index schema as a dictionary.
        Return None if no schema found.
        """
        if self._is_direct_access_index():
            schema_json = self._direct_access_index_spec.get("schema_json")
            if schema_json is not None:
                return json.loads(schema_json)
        return None

        Return the index schema as a dictionary.
        Return None if no schema found.
        
llama-index-integrations/vector_stores/llama-index-vector-stores-databricks/llama_index/vector_stores/databricks/base.py