How to check "Categories supplied by Company" via supplier registration script?

Hi Experts,

There is a group of checkboxes in Supplier Registration form, with heading "Categories supplied by company". We have a requirement to check that user selects at least one of these checkboxes and another validation on custom fields based on the selected category. So I wrote a Script Definition on Supplier Registration (Class 147) Validate event. I tried to fetch the selected value using: doc.getCollnExternalCat(), doc.getCollnInternalCat() - but both these collections are empty.

When I check in RG for Class 147, I see that "Categories supplied by company" is mapped to Display Name Id "CATEGORIES" with Field Type Enumeration, Please see attachment - SupplierRegistration_RG_UIView.png. But this Enumeration is not a clickable link like other enumerations and I am not able to figure out a matching getter method in iAPI. Please help.

Thanks,

Gayathri