public function getStatusCode()
    {
        $headers = $this->getHeaders();
        if ($headers->has('http-code')) {
            // take into account possible 'follow location'
            $statusCodeHeaders = $headers->get('http-code', null, false);
            return empty($statusCodeHeaders) ? null : end($statusCodeHeaders);
        }
        throw new Exception('Unable to get status code: referred header information is missing.');
    }