code: public PlainDate at(Weekday dayOfWeek) {
  
          if (dayOfWeek == Weekday.MONDAY) {
              return this.start.getTemporal(); // short cut
          }
  
          return PlainDate.of(this.year, this.week, dayOfWeek);
  
      }
docs: /*[deutsch]
  <p>Kombiniert diese Kalenderwoche mit dem angegebenen Wochentag zu einem Kalenderdatum. </p>
  
  @param   dayOfWeek       day of week in range MONDAY - SUNDAY
  @return  calendar date
  @throws  IllegalArgumentException if the result is beyond the maximum of date axis (exotic edge case)