void start() {
   connection.setErrorHandler(
       th -> {
         log.debug("QUIT failed, ignoring exception", th);
         resultHandler.handle(null);
       });
   connection.write(
       "QUIT",
       message -> {
         log.debug("QUIT result: " + message);
         if (!StatusCode.isStatusOk(message)) {
           log.warn("quit failed: " + message);
         }
         resultHandler.handle(null);
       });
 }