Click Controller's fullscreen icon. will pop nullpointerexception,please help to resolved it, thank you #68

// uvv_fitXY：视频拉伸适配video_view的尺寸
// uvv_autoRotation：根据方向传感器自动切换横竖屏
// uvv_scalable：显示或隐藏缩放按钮

private FrameLayout video_layout;
private LinearLayout button_layout;
private UniversalVideoView video_view;
private UniversalMediaController media_controller;
private Button start;
private TextView introduction;

private static final String TAG = "MainActivity16";
private static final String SEEK_POSITION_KEY = "SEEK_POSITION_KEY";
private static final String VIDEO_URL = "https://media.w3.org/2010/05/sintel/trailer.mp4";

private int mSeekPosition;
private int cachedHeight;
private boolean isFullScreen;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main16);
    getSupportActionBar().hide();
    getWindow().addFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN);

    initView();
    setVideoAreaSize();
    video_view.setVideoViewCallback(this);

    start.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            if (mSeekPosition > 0) {
                video_view.seekTo(mSeekPosition);
            }
            video_view.start();
            media_controller.setTitle("Game trailer video playing……");
        }
    });

    video_view.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {
        @Override
        public void onCompletion(MediaPlayer mediaPlayer) {
            Log.d(TAG, "Video On Completion……");
        }
    });

}

/**
 * 设置视频区域大小
 */
private void setVideoAreaSize() {
    video_layout.post(new Runnable() {
        @Override
        public void run() {
            int width = video_layout.getWidth();
            cachedHeight = (int) (width * 405f / 720f);

@Override
protected void onPause() {
    super.onPause();
    Log.d(TAG, "Video On Pause……");
    if (video_view != null && video_view.isPlaying()) {
        mSeekPosition = video_view.getCurrentPosition();
        Log.d(TAG, "Video On Pause mSeekPosition……" + mSeekPosition);
        video_view.pause();
    }
}

@Override
protected void onSaveInstanceState(@NonNull Bundle outState) {
    super.onSaveInstanceState(outState);
    Log.d(TAG, "Video On Save Instance State Position=" + video_view.getCurrentPosition());
    outState.putInt(SEEK_POSITION_KEY, mSeekPosition);
}

@Override
protected void onRestoreInstanceState(@NonNull Bundle savedInstanceState) {
    super.onRestoreInstanceState(savedInstanceState);
    mSeekPosition = savedInstanceState.getInt(SEEK_POSITION_KEY);
    Log.d(TAG, "Video On Restore Instance State Position=" + mSeekPosition);
}

private void initView() {
    video_layout = findViewById(R.id.video_layout);
    video_view = findViewById(R.id.video_view);
    media_controller = findViewById(R.id.media_controller);
    start = findViewById(R.id.start);
    introduction = findViewById(R.id.introduction);
    button_layout = findViewById(R.id.button_layout);

}

@Override
public void onScaleChange(boolean isFullscreen) {
    this.isFullScreen = isFullscreen;
    if (isFullscreen) {
        ViewGroup.LayoutParams layoutParams = video_layout.getLayoutParams();
        layoutParams.width = ViewGroup.LayoutParams.MATCH_PARENT;
        layoutParams.height = ViewGroup.LayoutParams.MATCH_PARENT;
        video_layout.setLayoutParams(layoutParams);
        button_layout.setVisibility(View.GONE);
    } else {
        ViewGroup.LayoutParams layoutParams = video_layout.getLayoutParams();
        layoutParams.width = ViewGroup.LayoutParams.MATCH_PARENT;
        layoutParams.height = this.cachedHeight;
        video_layout.setLayoutParams(layoutParams);
        button_layout.setVisibility(View.VISIBLE);
    }
    switchTitleBar(!isFullscreen);
}

private void switchTitleBar(boolean b) {
    ActionBar supportActionBar = getSupportActionBar();
    if (supportActionBar != null) {
        if (b) {
            supportActionBar.show();
        } else {
            supportActionBar.hide();
        }
    }
}


@Override
public void onPause(MediaPlayer mediaPlayer) {
    Log.d(TAG, "Video On Pause UniversalVideoView callback");
}

@Override
public void onStart(MediaPlayer mediaPlayer) {
    Log.d(TAG, "Video On Start UniversalVideoView callback");
}

@Override
public void onBufferingStart(MediaPlayer mediaPlayer) {
    Log.d(TAG, "Video On Buffering Start UniversalVideoView callback");
}

@Override
public void onBufferingEnd(MediaPlayer mediaPlayer) {
    Log.d(TAG, "Video On Buffering End UniversalVideoView callback");
}

@Override
public void onBackPressed() {
    if (this.isFullScreen) {
        video_view.setFullscreen(false);
    } else {
        super.onBackPressed();
    }
}