code: public Duration<CalendarUnit> getDuration(CalendarUnit... units) {
  
          PlainDate date = this.getTemporalOfOpenEnd();
          boolean max = (date == null);
  
          if (max) { // max reached
              date = this.getEnd().getTemporal();
          }
  
          Duration<CalendarUnit> result =
              Duration.in(units).between(
                  this.getTemporalOfClosedStart(),
                  date);
  
          if (max) {
              return result.plus(1, CalendarUnit.DAYS);
          }
  
          return result;
  
      }
docs: /*[deutsch]
  <p>Liefert die L&auml;nge dieses Intervalls in den angegebenen
  kalendarischen Zeiteinheiten. </p>
  
  @param   units   calendrical units as calculation base
  @return  duration in given units
  @throws  UnsupportedOperationException if this interval is infinite
  @since   2.0
  @see     #getLengthInDays()
  @see     #getDurationInYearsMonthsDays()