Add null check to work around async unregistration of receiver

    private final BroadcastReceiver mBroadcastReceiver = new BroadcastReceiver() {

        @Override

        public void onReceive(Context context, Intent intent) {

            // This receiver is unregistered when the view is detached, but on devices with multiple

            // displays, it can sometimes still receive an ACTION_SCREEN_ON/ACTION_SCREEN_OFF on

            // display switch, after it was detached, so this null check ensures no crash in that

            // scenario.

            // TODO(193941146): Currently unregistering a receiver through BroadcastDispatcher is

            // async, but we've already cleared the fields. Just return early in this case.

            if (mNavigationBarView == null) {

                return;

            }