code: public final void addListener(@NonNull final HideViewOnScrollAnimationListener listener) {
          Condition.INSTANCE.ensureNotNull(listener, "The listener may not be null");
          listeners.add(listener);
      }
docs: Adds a new listener, which should be notified about the animation's internal state, to the
  animation.
  
  @param listener
  The listener, which should be added, as an instance of the type {@link
  HideViewOnScrollAnimationListener}. The listener may not be null