gistfile1.py

class History(models.Model):
    changed_by = models.ForeignKey('user.CustomUser', null=True, blank=True)

    history = HistoricalRecords()

    @property
    def _history_user(self):
        return self.changed_by

    @_history_user.setter
    def _history_user(self, value):
        self.changed_by = value


class CustomUser(AbstractBaseUser, PermissionsMixin, History):

  ....