Format Empty

This one's probably been asked before but I'm tired of trying to find a
solution (if there is one!). I have an asp update page and I'd like to
convert all empty fields to NULL prior to updating the Access db rather than
permitting zero length fields in the db.

Is this possible? Is there any way
to globally declare this for all text fields on the asp page rather than
having to do a whole whack of "if then" formats? Is there something I can
set in the field's properties in Access that will deny zero length yet won't
cause the asp update to choke and return an error?