code: public static PeriodDuration of(Duration duration) {
          Objects.requireNonNull(duration, "The duration must not be null");
          return new PeriodDuration(Period.ZERO, duration);
      }
docs: Obtains an instance based on a duration.
  <p>
  The period will be zero.
  
  @param duration  the duration, not null
  @return the combined period-duration, not null