/**
  * Connect to Stomp server, if not connected.
  *
  * @throws \FuseSource\Stomp\Exception\StompException
  */
 protected function connect()
 {
     if (!$this->stomp->isConnected()) {
         $this->stomp->connect(Arr::get($this->credentials, 'username', ''), Arr::get($this->credentials, 'password', ''));
     }
 }