Test isnull{your.datefield} before doing anything else. Though I'm surprised you get a false date, on Crystal 8.5 one would get nothing.
I'm assuming that "field is empty" means null. If it were zeros, that might be seen as a date. In that case you could check your.datefield < date(1900, 1, 1) or whatever the possible limit is on your database.
Madawc Williams
East Anglia
Great Britain