NullValidator - how to?

Hi all,

How am I supposed to use NullValidator when validation is not performed if field is empty (null or “”)?

I want to do my own ‘required’ validation but Vaadin does not call validators: filed is either required and has value to be validated or is not validated at all. That does make sense, but…

Is there any way to perform validation (NullValidator, CustomValidator) on empty fields?