def json(self):
        """Returns de-JSONed data or None if it's a different content type."""
        if self._data_json:
            return self._data_json

        if not self.data or self.content_type != 'application/json':
            return None

        self._data_json = json.loads(self.data)
        return self._data_json
Returns de-JSONed data or None if it's a different content type.