1119: Access of possibly undefined property nativeWindow through a reference with static type flash.display:Stage.

i was trying this code :

http://help.adobe.com/en_US/as3/dev/WS5b3ccc516d4fbf351e63e3d118666ade46-7e08.html

but it shows error : 1119: Access of possibly undefined property nativeWindow through a reference with static type flash.display:Stage.

package

{

  import flash.display.Sprite;

  import flash.events.MouseEvent;

  import flash.text.TextField;

  public class MinimizeExample extends Sprite

  {

  public function MinimizeExample():void 

  {

  var minTextBtn:TextField = new TextField();

  minTextBtn.x = 10;

  minTextBtn.y = 10;

  minTextBtn.text = "Minimize";

  minTextBtn.background = true;

  minTextBtn.border = true;

  minTextBtn.selectable = false;

  addChild(minTextBtn);

  minTextBtn.addEventListener(MouseEvent.CLICK, onMinimize);

  var maxTextBtn:TextField = new TextField();

  maxTextBtn.x = 120;

  maxTextBtn.y = 10;

  maxTextBtn.text = "Maximize";

  maxTextBtn.background = true;

  maxTextBtn.border = true;

  maxTextBtn.selectable = false;

  addChild(maxTextBtn);

  maxTextBtn.addEventListener(MouseEvent.CLICK, onMaximize);

  var restoreTextBtn:TextField = new TextField();

  restoreTextBtn.x = 230;

  restoreTextBtn.y = 10;

  restoreTextBtn.text = "Restore";

  restoreTextBtn.background = true;

  restoreTextBtn.border = true;

  restoreTextBtn.selectable = false;

  addChild(restoreTextBtn);

  restoreTextBtn.addEventListener(MouseEvent.CLICK, onRestore);

  var closeTextBtn:TextField = new TextField();

  closeTextBtn.x = 340;

  closeTextBtn.y = 10;

  closeTextBtn.text = "Close Window";

  closeTextBtn.background = true;

  closeTextBtn.border = true;

  closeTextBtn.selectable = false;

  addChild(closeTextBtn);

  closeTextBtn.addEventListener(MouseEvent.CLICK, onCloseWindow);

  }

  function onMinimize(event:MouseEvent):void

  {

  this.stage.nativeWindow.minimize();

  }

  function onMaximize(event:MouseEvent):void

  {

  this.stage.nativeWindow.maximize();

  }

  function onRestore(event:MouseEvent):void

  {

  this.stage.nativeWindow.restore();

  }

  function onCloseWindow(event:MouseEvent):void

  {

  this.stage.nativeWindow.close();

  }

  }

}