code: @Deprecated
      public void sync(final Runnable runnable) {
          clientConnector.send(new EmptyCommand(), new OnFinishedHandler() {
              public void onFinished() {
                  runnable.run();
              }
  
          });
      }
docs: both java- and groovy-friendly convenience method to withContent an empty command, which will have no
  presentation models nor data in the callback