Matching an empty field?

I need to identify messages that have either the word "subject" or have
nothing at all in the subject field. Testing for nothing is puzzling me. I
went through the grep man page and procmailex but didn't see anything
useful. Do the following make sense?

* ^Subject: .*subject
* ^Subject: !.+

I don't know whether one can invert the sense of part of a condition like
that. This would obviously be useless:

* ! ^Subject: .+

Thanks,


--Ken
           68 Westy, Admin -- type2 -- The VW Bus Mailing List