code: public boolean isShorterThan(ReadableDuration duration) {
          if (duration == null) {
              duration = Duration.ZERO;
          }
          return compareTo(duration) < 0;
      }
docs: Is the length of this duration shorter than the duration passed in.
  <p>
  The comparison takes into account the sign.
  As such, a duration of <i>minus</i> 5 seconds is shorter than a duration of 3 seconds.
  
  @param duration  another duration to compare to, null means zero milliseconds
  @return true if this duration is strictly shorter than the duration passed in