there isn't a way, that I know of. You should have defined the field in the xsd file that is the structure of the data that the report bill using. If it is in the structure, then Crystal will see it as a NULL value, if the field is not in the structure, you can't use it in the report. If you developed the report with one structure and send another, you will get this sort of error.
I don't believe that Crystal was designed to handle changing structures (you can't add or subtract fields dynamically), so the field is always there.
I would ensure that the structure of your data matches the structure that Crystal is expecting.
HTH