code: @Nullable
      private ViewPropertyAnimator createAnimator(@NonNull final View animatedView,
                                                  @NonNull final RectangleRevealAnimation animation,
                                                  @Nullable final AnimatorListener listener) {
          if (animation.getX() != null || animation.getY() != null || animation.getWidth() != null ||
                  animation.getHeight() != null || animation.getAlpha() != null) {
              return animatedView.animate().setInterpolator(animation.getInterpolator())
                      .setDuration(getDuration(animatedView, animation))
                      .setStartDelay(animation.getStartDelay()).setListener(listener);
          }
  
          return null;
      }
docs: Creates an animator, which should be used for a rectangular reveal animation.
  
  @param animatedView
  The animated view as an instance of the class {@link View}. The view may not be null
  @param animation
  The animation as an instance of the class {@link RectangleRevealAnimation}. The
  animation may not be null
  @param listener
  The listener, which should be notified about the animation's events, as an instance
  of the type {@link AnimatorListener} or null, if no listener should be notified
  @return The animator, which has been created, as an instance of the class {@link
  ViewPropertyAnimator} or null, if no animation should be used