Using ASL in Requisitioner just on Categories, no items?

Looking at the UGs it seems I should be able to use ASLs by Commodity to then give the list of approved vendors in my shopping card on a custom Smart Form.

However, in testing just on Commodity, with no Item listed the Supplier LOV is coming up as NULL when I try this.

Steps taken,

Purchasing Super User: Supply Base > Approved Supplier List

Commodity - 1 loaded with 2 vendors, one status New, one status Approved with with the site in say X (OU).

Not linked to any blankets / release methods or UOMs.

iProcurement Catalog Admin

Stores > Smart Forms > New - Use "Restrict Suppliers = Category ASL".