code: public static ShortDuration of(long duration, TimeUnit unit) {
      if (duration == 0) {
        return ZERO;
      }
      checkArgument(duration >= 0, "negative duration: %s", duration);
      checkArgument(duration <= MAXES.get(unit),
          "ShortDuration cannot exceed 100 days: %s %s", duration, unit);
      long nanos = TimeUnit.NANOSECONDS.convert(duration, unit);
      return new PositiveShortDuration(nanos * 1000);
    }
docs: Factories