.clone() method in jquery without copying value

Possible Duplicate:
Jquery clone of a textbox without the content

I use .clone in jQuery. When I clone ul it is cloning its value also. I only want to copy structure not value. When you type some value in input field and then click clone it will clone input value too.

Here is my code snippet:

<div class="str">
    <ul><li><input type="text" /></li></ul>
</div>
<a href="#">clone</a>

$(function() {
    $('a').live('click', function() {
        var cln = $('ul:last').clone();
        $('.str').append(cln);
    });
});