Django 1.7.2迁移错误（AttributeError）

Question

运行数据迁移时，这是错误：

Running migrations:
  Applying bird_monitoring.0027_auto_20150327_1102...Traceback (most recent call last):
  File "/home/john/.virtualenvs/Client/lib/python3.4/site-packages/django/db/models/fields/related.py", line 555, in __get__
    rel_obj = getattr(instance, self.cache_name)
AttributeError: 'Locality' object has no attribute '_owner_cache'

During handling of the above...

“位置”具有属性所有者：

owner = models.ForeignKey(settings.AUTH_USER_MODEL, verbose_name='Owner', blank=True, null=True, on_delete=models.SET_NULL)

配置：Ubuntu，Python 3.4，Django 1.7.2，SQLite

谢谢你的帮助！

更新：“目标”模型：

class CampaignRegistration(models.Model):
    campaign = models.ForeignKey(Campaign, verbose_name='campaign')
    scrutineer = models.ForeignKey(settings.AUTH_USER_MODEL, verbose_name='scrutineer')
    locality = models.ForeignKey(Locality, verbose_name='locality')

迁移代码：

def transfer_become_scrutineers(apps, schema_editor):

    Campaign = apps.get_model("app", "Campaign")
    Locality = apps.get_model("app", "Locality")
    CampaignRegistration = apps.get_model("app", "CampaignRegistration")

    campaign = Campaign.objects.get(pk=1)

    for locality in Locality.objects.all():
        if locality.owner is None:
            pass
        else:
            registration = CampaignRegistration()
            ...
            registration.save()