missing information from API: min_delivery_days and max_delivery_days

[baa y]

Hi,

When getting shipping information in form of shipping profile destinations via a direct API call or an association request, the min and max_delivery_days fields return "null" if a shipping carrier and mail class is selected. Only for user entered values, we get non null values back. 

How can we get the missing delivery days values for various shipping carriers?

Thanks in advance and best wishes,

baa