setEmptyCellValue for BOOLEAN field doesn't work?

[Fantast]

Hi, I'm using smartgwt-2.4 on Firefox 4.

I'm trying to use ListGrid's setEmptyCellValue functionality for field with type ListGridFieldType.BOOLEAN. The problem is that null boolean value is rendered just as false value (i. e. as a unchecked CheckBox) instead of showing the ""emptyCellValue".
Here is the basic code snippet...

        ListGridField someField = new ListGridField("some", "Some thing" );
        someField.setType(ListGridFieldType.BOOLEAN);
        someField.setEmptyCellValue("--");

Can you please advice how to easily treat "null" values as "empty" for BOOLEAN fields?



Thanks