Is there a problem with this formula?

I want to test for a blank date field, but isnull(date field) is not evaluating as a null when the field is, in fact, empty. I have Convert Database Null Values to Default checked because I need it checked for other purposes in my report.

As an alternative, I'm using the following formula. Is this equivalent to isnull(date field)?

If length(cstr(date field)) = 0 then "null"

Else (date field)

Is there any scenario under which this this formula would not work?

I'd appreciate any feedback.

Gary