code: public RetryBuilder delay(Delay delay, Scheduler scheduler) {
      this.delay = (delay == null) ? Retry.DEFAULT_DELAY : delay;
      this.scheduler = scheduler;
      return this;
    }
docs: Set both the {@link Delay} and the {@link Scheduler} on which the delay is waited.
  If the delay is null, {@link Retry#DEFAULT_DELAY} is used.