constructor() {
    /**
     * The short error code.
     * @type {string}
     */
    this.code;
    /**
     * The human-readable error message.
     * @type {string}
     */
    this.message;
    /**
     * The HTTP error code number.
     * @type {number|undefined}
     */
    this.httpErrorCode;
    /**
     * The underlying reason error if available.
     * @type {!Error|undefined}
     */
    this.reason;
  }
The CIAP Error interface. If the error is recoverable, it will have a retry
callback on the object.
@interface