Chosenbox smart update emptyMessage doesn't work

<zk>
   <label multiline="true">
      1. click button to update empty message.
      2. you should see empty message is 'none'.
   </label>   <chosenbox id="cb" emptyMessage="empty..."/>
   <button label="update emptyMessage" onClick='cb.setEmptyMessage("none");'/>
   <zscript>
      String[] items = {
        "item 1", "item 2"
      };
      ListModel dictModel = new SimpleListModel(items);
      cb.setModel(dictModel);
   </zscript>
</zk>