Django 1.8迁移-“ NoneType”对象没有属性“ _meta”

尝试将项目从Django 1.7迁移到1.8。在解决了代码错误之后，我能够运行迁移。但是，当我尝试迁移时，出现错误“'NoneType'对象没有属性'_meta'”

追溯中没有任何我的应用程序的引用，因此我不确定寻找错误的确切位置（以及此处包含的代码，因此对那些试图帮助我的人会有所帮助）

这是追溯的全文

(venv)rtownley@ubuntu:~/Projects/sparrow1/NJ$ ./manage.py makemigrations
No changes detected
(venv)rtownley@ubuntu:~/Projects/sparrow1/NJ$ ./manage.py migrate
Operations to perform:
  Synchronize unmigrated apps: staticfiles, editor, djcelery, messages, getty, kombu_transport_django, debug_toolbar, utils, locking, petro, tokenapi, grappelli, django_extensions, selectable
  Apply all migrations: adops, taxonomy, issues, editorial, contenttypes, authors, auth, comms, membership, sessions, bento, urlalias, accounts, breaking_news, easy_thumbnails, images, admin, pages, documents, events
Synchronizing apps without migrations:
  Creating tables...
    Running deferred SQL...
  Installing custom SQL...
Running migrations:
  Rendering model states...Traceback (most recent call last):
  File "./manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/home/rtownley/Projects/sparrow1/venv/lib/python3.4/site-packages/django/core/management/__init__.py", line 338, in execute_from_command_line
    utility.execute()
  File "/home/rtownley/Projects/sparrow1/venv/lib/python3.4/site-packages/django/core/management/__init__.py", line 330, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/home/rtownley/Projects/sparrow1/venv/lib/python3.4/site-packages/django/core/management/base.py", line 390, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/home/rtownley/Projects/sparrow1/venv/lib/python3.4/site-packages/django/core/management/base.py", line 441, in execute
    output = self.handle(*args, **options)
  File "/home/rtownley/Projects/sparrow1/venv/lib/python3.4/site-packages/django/core/management/commands/migrate.py", line 221, in handle
    executor.migrate(targets, plan, fake=fake, fake_initial=fake_initial)
  File "/home/rtownley/Projects/sparrow1/venv/lib/python3.4/site-packages/django/db/migrations/executor.py", line 104, in migrate
    state = migration.mutate_state(state, preserve=do_run)
  File "/home/rtownley/Projects/sparrow1/venv/lib/python3.4/site-packages/django/db/migrations/migration.py", line 83, in mutate_state
    operation.state_forwards(self.app_label, new_state)
  File "/home/rtownley/Projects/sparrow1/venv/lib/python3.4/site-packages/django/db/migrations/operations/fields.py", line 51, in state_forwards
    state.reload_model(app_label, self.model_name_lower)
  File "/home/rtownley/Projects/sparrow1/venv/lib/python3.4/site-packages/django/db/migrations/state.py", line 97, in reload_model
    related_models = get_related_models_recursive(old_model)
  File "/home/rtownley/Projects/sparrow1/venv/lib/python3.4/site-packages/django/db/migrations/state.py", line 57, in get_related_models_recursive
    rel_app_label, rel_model_name = rel_mod._meta.app_label, rel_mod._meta.model_name
AttributeError: 'NoneType' object has no attribute '_meta'

其他可能发挥作用的部分：-我有一个自定义处理程序，可监听save事件，序列化数据并在Mongo中创建相同的对象-在运行Python3.4的虚拟环境中运行

有什么想法去寻找错误？谢谢，抱歉，我无法提供更多代码！