The value can not be stored as null although the inputing value does not exist in the drop-down list. But if you type something on the inputing box and then press 'ENTER' to do the selection action, the un-existing value will be cleared. If you have a strict rule to prevent from this issue, you can bind a 'blur' event to the inputing box to trigger the 'ENTER' keydown event.
$('#cc').combobox({
inputEvents: $.extend({}, $.fn.combobox.defaults.inputEvents, {
blur: function(){
var event = new $.Event('keydown');
event.keyCode = 13;
$(this).trigger(event)
}
})
})
The solution can be found in
http://www.jeasyui.com/forum/index.php?topic=5381.0