[flexcoders] Error while doing the Linked list demo using flex

[raji]

Hello sir,
               i am getting the error when i am running the code
           
           
            stage.scaleMode = StageScaleMode.NO_SCALE;
           
            stage.align = StageAlign.TOP_LEFT;
           
            dll = new DLinkedList();
           
            for (var i:int = 0; i < START_NODES; i++)
            {
                Alert.show("i am in forloop");
                var node:Node = new Node();
                //var node:UIComponent = new UIComponent();
                trace(node);
                node.removeEventListener(MouseEvent.MOUSE_UP,   
node.mouseHandler);
                trace(node.removeEventListener(MouseEvent.MOUSE_UP,   
node.mouseHandler));
                Alert.show("i am in outside loop");
                 addChild(node);
                trace(addChild(node));
                dll.append(node);
            }
           
            addChild(canvas = new Shape());
       

TypeError: Error #1009: Cannot access a property or method of a null object 
reference.
    at TestLinkedList/List()[C:\Users\raji\Documents\Flex Builder 
3\DataStrucutres\src\TestLinkedList.mxml:58]
    at TestLinkedList/init()[C:\Users\raji\Documents\Flex Builder 
3\DataStrucutres\src\TestLinkedList.mxml:34]
    at 
TestLinkedList/___TestLinkedList_Application1_creationComplete()[C:\Users\raji\Documents\Flex
 Builder 3\DataStrucutres\src\TestLinkedList.mxml:2]
    at flash.events::EventDispatcher/dispatchEventFunction()
    at flash.events::EventDispatcher/dispatchEvent()
    at 
mx.core::UIComponent/dispatchEvent()[C:\autobuild\3.2.0\frameworks\projects\framework\src\mx\core\UIComponent.as:9298]
    at mx.core::UIComponent/set 
initialized()[C:\autobuild\3.2.0\frameworks\projects\framework\src\mx\core\UIComponent.as:1169]
    at 
mx.managers::LayoutManager/doPhasedInstantiation()[C:\autobuild\3.2.0\frameworks\projects\framework\src\mx\managers\LayoutManager.as:718]
    at Function/http://adobe.com/AS3/2006/builtin::apply()
    at 
mx.core::UIComponent/callLaterDispatcher2()[C:\autobuild\3.2.0\frameworks\projects\framework\src\mx\core\UIComponent.as:8628]
    at 
mx.core::UIComponent/callLaterDispatcher()[C:\autobuild\3.2.0\frameworks\projects\framework\src\mx\core\UIComponent.as:8568]