The
add_ordering() method has a call to the
names_to_path() function with the following comment:
# names_to_path() validates the lookup. A descriptive
# FieldError will be raise if it's not.
self.names_to_path(item.split(LOOKUP_SEP), self.model._meta)
(django.db.models.sql.query: ~1989 line)
Function names_to_path have optional fail_on_missing argument, but is don't pass
(== fail_on_missing=False) in call from add_ordering.