When an externally described file contains null-capable fields and the
ALWNULL(*NO) keyword is specified on a control specification, the following
conditions apply:
A record containing null values retrieved from a file will cause a data
mapping error and an error message will be issued.
Data in the record is not accessible and none of the fields in the record
can be updated with the values from the input record containing null values.
With this option, you cannot place null values in null-capable fields
for updating or adding a record. If you want to place null values in null-capable
fields, use the ALWNULL(*USRCTL) option.