This is a known issue in IE8 which described here: http://blogs.msdn.com/b/jscript/archive/2009/06/23/serializing-the-value-of-empty-dom-elements-using-native-json-in-ie8.aspx

When trying to use JSON.stringify() to serialize the value of an empty DOM element. It returns "null" instead of "".

It would be better if JQuery can handle this issue.

Test code:

<div></div>

$('div').text('');
var t = $('div').text();

$('body').append(t);
$('body').append(JSON.stringify(t));