  MetadataMapVector* getRequestMetadataMapVector() {
    if (request_metadata_map_vector_ == nullptr) {
      request_metadata_map_vector_ = std::make_unique<MetadataMapVector>();
    }
    return request_metadata_map_vector_.get();
  }
  MetadataMapVector* getRequestMetadataMapVector() {
    if (request_metadata_map_vector_ == nullptr) {
      request_metadata_map_vector_ = std::make_unique<MetadataMapVector>();
    }
    return request_metadata_map_vector_.get();
  }