At this point, we don't know why this line of code is executed, but
we do know it's not consistently executed between Django 1.10 and
Django 1.11 due to the addition of `ForwardOneToOneDescriptor`, a
subclass of `ForwardManyToOneDescriptor`.
Refs. 6628145af7
Refs. kavdev/dj-stripe#524
Refs. django/django@38575b007a