Enhance exception type and message in FieldMap class setField method

[amin-moradi]

This is an enhancement. In class FieldMap, method setField(StringField field) throws a NullPointerException, but it does not mention which field: throw new NullPointerException("Null field values are not allowed.");

I would suggest to throw an exception like following to mention the field name and also a better exception type like FieldException: throw new FieldException(SessionRejectReason.NULL_DATA_FOR_VALUE, field.getField());

[chrjohn]

Sounds like a sensible enhancement. Are you able to provide a PR? Thanks

[vinipx]

Sounds like a sensible enhancement. Are you able to provide a PR? Thanks

@chrjohn I would like to give it a try to fix it :)

[chrjohn]

@vinipx great, thanks 👍