public function send(string $payload = null, string $header = null)
    {
        if (is_null($header)) {
            $this->relay->send($header, Relay::PAYLOAD_CONTROL | Relay::PAYLOAD_NONE);
        } else {
            $this->relay->send($header, Relay::PAYLOAD_CONTROL | Relay::PAYLOAD_RAW);
        }

        $this->relay->send($payload, Relay::PAYLOAD_RAW);
    }