The NULL XFD directive allows the specification of a value which would indicate a field's contents are to be treated as NULL in interactions with the DBMS. It enables Database Connectors to handle NULL values by comparing values when performing read and write actions on the database to determine and perform appropriate actions. This directive is only valid with non-key fields.
Specify the NULL XFD directive on individual fields within the COBOL FD.
During a write to the database, this directive compares the value of the COBOL field against its own set literal value. If the values are equal, it writes a NULL value to the database.
During a read of the database, if a NULL value is returned, this directive places the specified literal value into the COBOL field before returning to the COBOL program.