code: function toDefaultErrorResponseBody(error) {
    const json = error && error.toJSON();
    if (json) {
      if (json.httpStatus) {
        delete json.httpStatus; // don't really need `httpStatus` inside `body` too, since have it in response as `statusCode`
      }
      if (json.headers) {
        delete json.headers; // don't want error's `headers` inside `body`, since have more comprehensive `headers` in response
      }
    }
    return json;
  }
docs: A default conversion from an error to an error response body for a Lambda Proxy error response
  @param {AppError} error - an error to convert
  @return {Object} an error response body