title: tastypie POST method return an dict key is error but empty value
body: <p>I have a question about django tastypie, i want to POST data to the api,
  but it return 400, and the error message is empty
    My Resource is non-orm, so i override the obj_create method
    but the GET method work well.
    Here is my code</p>
  
  <pre><code>class DitcObject(object):
  
      def __init__(self, initial=None):
          self.__dict__['_data'] = {}
  
          if hasattr(initial, 'items'):
              self.__dict__['_data'] = initial
  
      def __getattr__(self, item):
          return self._data.get(item, None)
  
      def __setattr__(self, key, value):
          self.__dict__['_data'][key] = value
  
      def to_dict(self):
          return self._data
  
  class QueueResource(Resource):
  
      qid = fields.CharField(attribute='qid')
      queue = fields.CharField(attribute='queue')
  
      class Meta:
          resource_name = 'queue'
          object_class = DitcObject
          authorization = Authorization()
  
      def _client(self):
          return RedisTool().get_redis()
  
      def detail_uri_kwargs(self, bundle_or_obj):
          kwargs = {}
  
          if isinstance(bundle_or_obj, Bundle):
              kwargs['pk'] = bundle_or_obj.obj.qid
          else:
              kwargs['pk'] = bundle_or_obj.qid
  
          return kwargs
  
      def get_object_list(self, request):
          queues = filter(lambda item:re.match(r'%s_update_plan\..+\..+' % PRO_FLAG, item), self._client().keys())
          results = []
  
          for result in queues:
              new_obj = DitcObject(initial={'queue': list(self._client().smembers(result))})
              new_obj.qid = result
              results.append(new_obj)
  
          return results
  
      def obj_get_list(self, bundle, **kwargs):
          qid = bundle.request.GET.get('qid')
          if qid:
              return [obj for obj in self.get_object_list(bundle.request) if obj.qid == qid]
          return self.get_object_list(bundle.request)
  
      def obj_get(self, bundle, **kwargs):
          queue = self._client().smembers(kwargs['pk'])
  
          return DitcObject(initial={'queue': list(queue), 'qid': kwargs['pk']})
  
      def obj_create(self, bundle, **kwargs):
          bundle = self.full_hydrate(bundle)
          print kwargs
          return bundle
  </code></pre>
  
  <p>and this is my error return</p>
  
  <pre><code>HTTP/1.0 400 BAD REQUEST
  Date: Tue, 14 Jan 2014 09:20:35 GMT
  Server: WSGIServer/0.1 Python/2.7.3
  Content-Type: application/json
  
  {"error": ""}
  </code></pre>
  
  <p>thanks all!</p>