message: Use D | undefined
diff: @@ -82,7 +82,7 @@ export interface ResponseErrorLiteral<D> {
  export class ResponseError<D> extends Error {
  public readonly code: number;
  - public readonly data?: D;
  + public readonly data: D | undefined;
  constructor(code: number, message: string, data?: D) {
  super(message);
  