public function sendHeaders(ResponseInterface $response)
    {
        foreach ($response->getHeaders() as $header => $values) {
            $first = true;
            $header = HeaderHelper::normalizeHeaderName($header);

            foreach ($values as $value) {
                $this->header(sprintf('%s: %s', $header, $value), $first);

                $first = false;
            }
        }

        return $this;
    }