TwinColSelect exception on Form.commit() with BeanItemContainer

I’m using 6.3 nightly and must not be doing something right when using a TwinColSelect. I am able to populate it nicely so that I see the full list of choices on the left side, with the selected ones appearing on the right side.

But when I do a Form.commit(), I get an exception:$ConversionException: java.lang.NoSuchMethodException: java.util.HashSet.(java.lang.String)
	at com.vaadin.ui.AbstractField.commit(
	at com.vaadin.ui.Form.commit(

This should be auto-set on commit by my BeanItemContainer, which it is doing for all fields until it reaches the selection box.

My bean field that drives the selection list is:

	public HashSet<String> getPermGroupListIds() {
		return createIdHashSet( group.getPermGroupList(user()) );
	public void setPermGroupListIds(HashSet<String> v) {
		System.out.println("v.size: " + v.size());

I noted in the debugger that AbstractField.commit() calls:

The ‘newValue’ at this point is a Collections$UnmodifiableSet apparently of a HashSet type and shows a size of 2 (for the two I’ve selected and appear in the right side as normal).

There is a test in MethodProperty.setValue that says:

// Try to assign the compatible value directly
        if (newValue == null || type.isAssignableFrom(newValue.getClass())) {

But it fails this test, which is disappointing since it seems I support accepting a HashSet in my setPermGroupListIds() method. Then the exception is thrown on the call:

final Constructor constr = getType().getConstructor(
                        new Class[] { String.class });

What am I doing wrong with my bean’s set method to accept the values from the TwinColSelection?

Actually, think I figured out I just need to use Set and not HashSet as the argument types.