Initial migration failing

I get this error when the makefile runs the initial migration:

```
django.core.exceptions.FieldDoesNotExist: User_groups has no field named None
```

Maybe this cropped up in the latest version of Django?

I was able to work around this with:

```
  rm example/api/migrations/0001_initial.py*
  rm example/api/migrations/0002_auto_20150525_1522.py*
  ./manage.py makemigrations
```
