Dont understand what is wrong in code

Question

Task of my code that movieclip added on stage, change its size - height when change size of browsers(player) window thus height movieclip = height rowsers(player) window.
That is my code:
package
import flash.display.*;
import flash.display.Sprite;
import flash.display.StageAlign;
import flash.display.StageScaleMode;
import flash.events.Event;
public class ZhMenu extends Sprite
public var menubg:MovieClip;
public function ZhMenu()
var menubg:  = new menuGrad();
stage.scaleMode = StageScaleMode.NO_SCALE;
stage.align = StageAlign.TOP_LEFT;
stage.addEventListener(Event.RESIZE, onResize);
this.addChild (menubg);
menubg.x=0;
menubg.width = 150;
menubg.height = stage.stageHeight;
public function onResize (event:Event):void
var sh:Number = stage.stageHeight;
menubg.x=0;
menubg.width=150;
menubg.height=sh;
In the issue MovieClip menubg added on stage but when i change size of window i get error:
TypeError: Error #1009: It is not possible to cause property or a method referring to object "null".
at ZhMenu/onResize()
And menubg dont change its size of course.
I dont understand what is wrong.
Plize help me if u know Action Script 3.0 better.

Answer 1

Because you do not have an instance of the object... open a new fla and try these lines...
// this will fail
var menubg:MovieClip;
menubg.x = 0;
// this will not fail
var menubg2:MovieClip = new MovieClip();
menubg2.x = 0;