code: @Nullable
      public Animator onAppear(@NonNull ViewGroup sceneRoot,
                               @NonNull View view,
                               @Nullable TransitionValues startValues,
                               @Nullable TransitionValues endValues) {
          return null;
      }
docs: The default implementation of this method returns a null Animator. Subclasses should
  override this method to make targets appear with the desired transition. The
  method should only be called from
  {@link #onAppear(ViewGroup, TransitionValues, int, TransitionValues, int)}.
  
  @param sceneRoot The root of the transition hierarchy
  @param view The View to make appear. This will be in the target scene's View hierarchy and
  will be VISIBLE.
  @param startValues The target values in the start scene
  @param endValues The target values in the end scene
  @return An Animator to be started at the appropriate time in the
  overall transition for this scene change. A null value means no animation
  should be run.