Getting a TypeError exception on a post_collection call

[jimbobhickville]

    def post_collection(self, session, data, api_type):
        """
            Create a new Resource.

            :param session: SQLAlchemy session
            :param data: Request JSON Data
            :param params: Keyword arguments
            """
        model = self._fetch_model(api_type)
        self._check_json_data(data)

        orm_desc_keys = model.__mapper__.all_orm_descriptors.keys()

        if 'type' not in data['data'].keys():
            raise MissingTypeError()

        if data['data']['type'] != model.__jsonapi_type__:
            raise InvalidTypeForEndpointError(
                model.__jsonapi_type__, data['data']['type'])

        resource = model()
        check_permission(resource, None, Permissions.CREATE)

        data['data'].setdefault('relationships', {})
        data['data'].setdefault('attributes', {})

        data_keys = set(map((lambda x: resource.__jsonapi_map_to_py__.get(x, None)), data['data'].get('relationships', {}).keys()))
        model_keys = set(resource.__mapper__.relationships.keys())
        if not data_keys <= model_keys:
            raise BadRequestError(
                '{} not relationships for {}'.format(
                    ', '.join(list(data_keys -
>                                  model_keys)), model.__jsonapi_type__))
E           TypeError: sequence item 0: expected str instance, NoneType found

.tox/py35/lib/python3.5/site-packages/sqlalchemy_jsonapi/serializer.py:968: TypeError

I was attempting to POST an object with a one-to-many related object and hit this exception. I'm sure I'm doing something wrong as I'm new to jsonapi, but I wish it produced a better error message this.

[Anderycks]

Can you add the call you were trying to make? And maybe an example of the models/relationship?