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