Fix for crashing when function alias provided that has NoneType for inspect.getmodule(value)

[evgenyslab]

Generation crashes when using a model with a property as such:

from datetime import date
from model_utils.models import TimeStampedModel

class MyModel(TimeStampedModel):
   some_date = models.DateField(default=date.today, verbose_name="someDate")

^ this will crash because inspect.getmodule(value) when value = date.today returns NoneType which has no __name__.