Yes.  I had a 'create' auditor that did:

   users = db.category.get(category, 'add_as_nosy')

and the 'category' variable was None when the issue was first created
via the email interface.  So the error message I got in response to the
email was just that None was an unknown category variable, but without
the traceback I had no idea what code was trying to look up None.

I presume you would get the same kind of error if you try to look up
None on any existing property, such as 'priority', in a create auditor.