Field Validation in Flat File Schema in WebMethods 6.0.1

In Flat File schema, I need to do field level and record validations ,some fields and records are mandatory . Records can be set as mandatory by providing Required “R” in conditional validator but not able to make fields in record as mandatory , i have checked Mandatory but it did not help. I have noticed convertToValues is taking blank values for the fields the service is not nullifying so even it is mandatory, as the field is not null, it is not doing validation .
Is there any way to do the field level validation? How to nullify those fields any option provided in convertToValues service?