anchor.diff:    /// The `orientation` argument is a list of [DeviceOrientation] enum values.
     /// The empty list causes the application to defer to the operating system
     /// default.
  -  static Future<Null> setPreferredOrientations(List<DeviceOrientation> orientations) async {
  +  static Future<void> setPreferredOrientations(List<DeviceOrientation> orientations) async {
       await SystemChannels.platform.invokeMethod(
         'SystemChrome.setPreferredOrientations',
         _stringify(orientations),
  
positive.code:   ///
    /// On Android, the system UI cannot be changed until 1 second after the previous
    /// change. This is to prevent malware from permanently hiding navigation buttons.
    static Future<Null> restoreSystemUIOverlays() async {
      await SystemChannels.platform.invokeMethod(
        'SystemChrome.restoreSystemUIOverlays',
        null,
  
negative.code:   /// after a delay of 1 second. This can be achieved through [restoreSystemUIOverlays]
    /// or calling this again. Otherwise, the original UI overlay settings will be
    /// automatically restored only when the application loses and regains focus.
    static Future<void> setEnabledSystemUIOverlays(List<SystemUiOverlay> overlays) async {
      await SystemChannels.platform.invokeMethod(
        'SystemChrome.setEnabledSystemUIOverlays',
        _stringify(overlays),
  