public function send(Parameters $params)
    {
        $this->client->setUri(ReCaptcha::VERIFY_SERVER);
        $this->client->setRawBody($params->toQueryString());
        $this->client->setEncType('application/x-www-form-urlencoded');
        $result = $this->client->setMethod('POST')->send();
        return $result ? $result->getBody() : null;
    }