Filtering on a date field set to NULL

I am trying to create a filter on a TTABLE object that would only allow
records where a certain date field is equal to NULL. Unfortunately, it
does not seem that Delphi 2.0 allows for such an eventuality. running the
filter through a query works, but does not fit in with my current design.
Is there any way to filter on a NULL date field?

the text I am currently using is:

                Geoff Callaghan