flex 正则表达式对空字符串的诡异判断

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
				minWidth="955" minHeight="600" layout="absolute"
				creationComplete="application1_creationCompleteHandler(event)">
	<mx:Script>
		<![CDATA[
			import mx.events.FlexEvent;
			// when the RegExpValidator is set require = false and the test = "",it won't do the validator!
			protected function application1_creationCompleteHandler(event:FlexEvent):void
			{
				var regExp:RegExp = new RegExp("^[A-Za-z0-9]{1,8}$");
				trace(regExp.test("")); // false;
				trace(regExp.test(null)); // true !!!!!!!!!!!!!!!!!!!
			}
			
		]]>
	</mx:Script>
	
</mx:Application>