Tom Götz

Return an empty list and provide some user feedback using component.error("...")?

Hm, you could do the following: ``` java public class MySelect2Choice extends Select2Choice { public MySelect2Choice(String id, IModel model, ChoiceProvider provider) { super(id, model, provider); } @Override public void onResourceRequested()...

Hmm, let me think about that. @ivaynberg : You have a better idea?

Patches or pull requests are always welcome ;-)

But: can't you provide an (unique) id value for your EmailAddressHolder that enabled reconstruction in toChoices()? Meaning: where do you keep your list of EmailAddressHolders? Wouldn't it be enough to...

`ListUtils.union(list1, list2);` ?

So then, why can't you use the list index of your list of holder objects to generate the id? ``` java public abstract class MyChoiceProvider extends TextChoiceProvider { private IModel

Wicket does the same: storing the id of the list index in the client, see `org.apache.wicket.markup.html.form.ChoiceRenderer#getIdValue`. I can't see anything wrong with that approach, what is your concern?

Ok, I see your point. Are the email addresses unique? You could use those as id then.

No problem, simply do something like this: ``` java Select2MultiChoice multiChoice = new Select2MultiChoice( "multiChoice", model, choiceProvider); form.add(multiChoice); multiChoice.add(new AjaxEventBehavior("change") { @Override protected void onEvent(AjaxRequestTarget target) { // do something...