I am getting an error on this test:

```
======================================================================
ERROR: test_init (tests.cases.models.tests.DataQueryTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/ruthb/Code/cbmi/avocado/tests/cases/models/tests.py", line 259, in test_init
    self.assertEqual(query.context.json, json['context'])
  File "/Users/ruthb/Code/cbmi/avocado/avocado/query/models.py", line 148, in context
    return AbstractDataContext(json=self.context_json)
  File "/Users/ruthb/Code/cbmi/avocado/avocado/query/models.py", line 23, in __init__
    super(AbstractDataContext, self).__init__(*args, **kwargs)
  File "/Users/ruthb/.virtualenvs/apps/avocado/lib/python2.7/site-packages/django/db/models/base.py", line 405, in __init__
    setattr(self, field.attname, val)
  File "/Users/ruthb/.virtualenvs/apps/avocado/lib/python2.7/site-packages/jsonfield/subclassing.py", line 41, in __set__
    obj.__dict__[self.field.name] = self.field.pre_init(value, obj)
  File "/Users/ruthb/.virtualenvs/apps/avocado/lib/python2.7/site-packages/jsonfield/fields.py", line 52, in pre_init
    if obj._state.adding and obj.pk is not None:
  File "/Users/ruthb/.virtualenvs/apps/avocado/lib/python2.7/site-packages/django/db/models/base.py", line 466, in _get_pk_val
    return getattr(self, meta.pk.attname)
AttributeError: 'NoneType' object has no attribute 'attname'
```

It seems to want the primary key field, but I am not sure why..