List of assignees to the activity.

def assignees(self):
        """List of assignees to the activity."""
        if 'assignees' in self._json_data and self._json_data.get('assignees_ids') == list():
            return []
        elif 'assignees' in self._json_data and self._json_data.get('assignees_ids'):
            assignees_ids_str = ','.join([str(id) for id in self._json_data.get('assignees_ids')])
            return self._client.users(id__in=assignees_ids_str, is_hidden=False)
        return None