For jinja & JSON novices like me, here's what I finally figured out in order to deal with the error message that is thrown when a user has no role in the app and you're trying to populate a field with the role name property. I added a condition that checks to see if a role is returned, and then if so, populated with the role name property, and if not, populated with None. It took me forever to figure out the right syntax to get the expression to actually evaluate properly (I had to use the tojson filter to actually get a value to compare against), so hopefully this helps someone else as well.
Expression evaluates to TRUE:
{{quickbase_make_request_1.json.qdbapi.user.roles|tojson!='null'}}
If TRUE, then populates the Role field with {{quickbase_make_request_1.json.qdbapi.user.roles.role['name']}}
If FALSE then populates the Role field with 'None'
