code: public static UnsubscribeMessage createCleanupMessage(WebSocketSession session) {
  		UnsubscribeMessage msg = new UnsubscribeMessage("**");
  
  		msg.setWebSocketSessionId(session.getId());
  		msg.setPrincipal(session.getPrincipal());
  		msg.setWampSession(new WampSession(session));
  
  		msg.cleanup = true;
  
  		return msg;
  	}
docs: Creates an internal unsubscribe message. The system creates this message when the
  WebSocket session ends and sends it to the subscribed message handlers for cleaning
  up
  
  @param sessionId the WebSocket session id