public function send(RequestInterface $request)
    {
        $this->request = $request;

        if ($this->httpClient instanceof ClientInterface || method_exists($this->httpClient, 'send')) {
            $this->response = $this->httpClient->send($request);
        } else {
            throw new \RuntimeException('HTTP Client must implement method send, and return ResponseInterface');
        }

        return $this->response;
    }