# File lib/new_relic/agent/instrumentation/curb.rb, line 76
      def header_str_with_newrelic
        if self._nr_serial
          self._nr_header_str
        else
          # Since we didn't install a header callback for a non-serial request,
          # just fall back to the original implementation.
          header_str_without_newrelic
        end
      end