 
     private function initializeTypicalItem():void
     {
-        if (_typicalItem == null)
+        if (_typicalItem === null)
         {
             setTypicalLayoutElement(null);
             return;

     */
    public function set typicalItem(value:Object):void
    {
        if (_typicalItem == value)
            return;
        _typicalItem = explicitTypicalItem = value;
        typicalItemChanged = true;

        {
            var rendererFactory:IFactory = itemRendererFunction(item);
            
            // if the function returned a factory, use that.
            // otherwise, if it returned null, try using the item directly
            if (rendererFactory)
                myItemRenderer = rendererFactory.newInstance();
            else if (item is IVisualElement && item is DisplayObject)
                myItemRenderer = IVisualElement(item);
        }
        
        // 2. if itemRenderer is defined, instantiate one
