code: private void stopLevel234Containers() {
      if (level2 != null) {
        level2.stop();
        level2 = null;
        level3 = null;
        level4 = null;
      }
    }
docs: Stops level 2, 3 and 4 containers cleanly if they exists.
  Call this method before {@link #startLevel1Container()} to avoid duplicate attempt to stop safemode container
  components (since calling stop on a container calls stop on its children too, see
  {@link ComponentContainer#stopComponents()}).