docs: def not_found(entity_id=None, message='Entity not found'):
          """
          Build a response to indicate that the requested entity was not found.
  
          :param string message:
              An optional message, defaults to 'Entity not found'
          :param string entity_id:
              An option ID of the entity requested and which was not found
          :return:
              A flask Response object, can be used as a return type from service methods
          """
          resp = jsonify({'message': message, 'entity_id': entity_id})
          resp.status_code = 404
          return resp