Hello all,
I have encountered error while trying to Create Rename Table in Asset Package with the following errors:

This error suggesting that Subnetwork Field Name which created by system when running Add Tier tool should be not nullable. But I did noticed that Add Tiers tools will create a Subnetwork Field Name that accept nulls value (I was just trying to add one more tier in the single-user Utility Network).

Was wondering why is it so? And how to ensure Subnetwork Field Name created is not nullable.
Thanks in advance!