No, there is no way to really do this. However, depending on which version of Crystal you're using, you should be able to turn on "Use Default Values for Null" in the formula editor for calculations like these so that you don't have to explicitly check for null. If you don't see data when you expect to, open the formula in the formula editor and change "Exceptions for Nulls" to "Default Values for Nulls" in the menu button bar at the top.
You can also set that option as a default for new reports/formulas by going to the File menu - select "Options" then "Formula Editor" and look for "Null Treatment". I don't think this will override existing formulas, but it will set it as a default for anything new.
-Dell