问Django - 'NoneType‘对象没有'year’属性

EN

class Profile(models.Model):
    date_of_birth = models.DateField()

    def age(self):
        import datetime
        if self.date_of_birth:
            dob = self.date_of_birth
            tod = datetime.date.today()
            my_age = (tod.year - dob.year) - int((tod.month, tod.day) < (dob.month, dob.day))
            return my_age
        else:
            return ''