public function sendBulkMessages(array $messages, array $params = null)
    {
        $sender = $this->createBulkSender();
        v::notEmpty()->setName("BulkSms Array")->check($messages);

        foreach ($messages as $message) {
            // make sure messages are proper objects
            v::instance('anlutro\BulkSms\Message')->check($message);
            $sender->addMessage($message);
        }

        if ($params) {
            $sender->setParams($params);
        }
        $response = $sender->send($this->testMode);
        $this->validateResponse($response);

        return $sender->extractResponse($response);
    }