protected function call()
    {
        $curl = curl_init();

        curl_setopt_array($curl, array(
            CURLOPT_RETURNTRANSFER      => 1,
            CURLOPT_URL                 => $this->requestUrl[$this->format].$this->param,
            CURLOPT_SSL_VERIFYPEER      => false,
            CURLOPT_FAILONERROR         => true,
        ));

        $request = curl_exec($curl);

        if (empty($request)) {
            throw new \RuntimeException('cURL request retuened following error: '.curl_error($curl) );
        }

        curl_close($curl);

        return $request;
    }