flex 移除dataprovider里的项目时,ItemRenderer set方法传值为null

<?xml version="1.0" encoding="utf-8"?>
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009" 
			   xmlns:s="library://ns.adobe.com/flex/spark" 
			   xmlns:mx="library://ns.adobe.com/flex/mx" minWidth="955" minHeight="600" creationComplete="init(event)">
	<s:layout>
		<s:VerticalLayout/>
	</s:layout>
	<fx:Script>
		<![CDATA[
			import com.crap.vo.Teacher;
			
			import mx.collections.ArrayCollection;
			import mx.events.FlexEvent;
			
			[Bindable]
			private var teacherAC:ArrayCollection=new ArrayCollection();
			
			protected function init(event:FlexEvent):void
			{
				var teacher:Teacher=new Teacher();
				teacher.name="name1";
				teacherAC.addItem(teacher);
				
				teacher=new Teacher();
				teacher.name="name2";
				teacherAC.addItem(teacher);
			}
			
			protected function bar(event:MouseEvent):void
			{
				teacherAC.removeItemAt(0);
			}
			
		]]>
	</fx:Script>
	<s:Button click="bar(event)" label="abc"/>
	<s:DataGroup dataProvider="{teacherAC}">
		<s:itemRenderer>
			<fx:Component>
				<s:ItemRenderer>
					<fx:Script>
						<![CDATA[
							public override function set data(data:Object):void{
								trace(data);
							}
						]]>
					</fx:Script>
				</s:ItemRenderer>
			</fx:Component>
		</s:itemRenderer>
	</s:DataGroup>
</s:Application>

上面代码中,当点击了按钮以后,DataGroup的dataProvider的ArrayCollection少了一个项目,这样会触发DataGroup的itemRemoved方法,
里面有

if (oldRenderer is IDataRenderer && oldRenderer !== item)
            IDataRenderer(oldRenderer).data = null;
           
这样就是向ItemRenderer的data setter中传了一个null,不注意的情况下,很容易抛空指针异常.