Skip setting the controller if the animation is already finished

            @Override

            public void onRecentsAnimationStart(RecentsAnimationController controller,

                    RecentsAnimationTargets targets) {

                if (mCallbacks == null) {

                    // It's possible for the recents animation to have finished and be cleaned up

                    // by the time we process the start callback, and in that case, just we can skip

                    // handling this call entirely

                    return;

                }

                mController = controller;

                mTargets = targets;

            }