Calculate NULL FacilityID for newly created row when line is split

[JimGrimes]

When splitting lines in a versioned Utilities gdb, I'm looking to keep all the attributes the same in the newly created line, except for the FacilityID. I'd like to have the value calculate to NULL at the time of the split for the new row in the table and maintain all the other attributes as it currently works. Trying to accomplish this with the Attribute Assistant and the Expression or Field Trigger rules, any ideas?

Maybe incorporating the Assign Default To Field expression, but not sure how to configure in Attribute Assistant.  https://desktop.arcgis.com/en/arcmap/latest/tools/data-management-toolbox/assign-default-to-field.ht...

[JoeBorgione]

You are using Attribute Assistant and not Attribute Rules which are an entirely different beast.  I used Attribute Assistant a couple years ago for a while and have since migrated to Attribute Rules in which I have done just what you are describing.  Sorry, can't help you with Attribute Assistant.