URGENT: listBox default value

[Angelistis]

i used this function on a listBox (I used this and not the comboBox because the size of my swf) to load the XML:

[I]function OnLoadNature() {
oRoot = natureList.lastChild;
oCliList = oRoot.lastChild;
nat.removeAll();
nat.addItem("Any", "");
for (var i = 0; i<oCliList.childNodes.length; i++) {
nat.addItem(oCliList.childNodes[i].firstChild.nodeValue, oCliList.childNodes.attributes.ID);
}
}


but, the listBox don't select any option by default, so when, you click on the button, it returns a "undefined" value... what can I do to have a default item? is this case, the item named "Any".