Release strategy check for filled field

Hi,

I have setup the release strategies for PO. I want to have a check if the PO is created with refrence to a contract. So if the field konnr is not empty, the release strategy should be triggered.

My problem exist during classification of the release strategy. I can give the characteristicc KONNR a value but there is no option to say 'IF KONNR IS EMPTY'. Is it possible to arrange this?

Thanks in advance for any answers

Regards,

Roel van Loon