Thank you DenesL, I did't know about IS_EMPTY_OR validator and it is what I was looking for.
The answer to my second question is only working for the first time the page is shown. It will not allow to change the client. I guess the only way to have dynamic combo's is via ajax (when user selects a client get all projects via ajax and populate the project combo). At least this is the only way I could solve my second question. Thanks again, rif
