$('#Test').val(null); IE vs. the rest

Hi guys
I have the following case:
<input type="text" id="Test" />
<script>
$('#Test').val(null);
</script>
See working example here:
http://jquery.nodnod.net/cases/421
In IE (i have tested in IE7), it puts the words null into the textbox
in all other browsers it puts nothing into the textbox. Why is this???
Cheers
Anthony