docs: public Duration withDurationAdded(long durationToAdd, int scalar) {
          if (durationToAdd == 0 || scalar == 0) {
              return this;
          }
          long add = FieldUtils.safeMultiply(durationToAdd, scalar);
          long duration = FieldUtils.safeAdd(getMillis(), add);
          return new Duration(duration);
      }