code: public static CalendarYear from(GregorianDate date) {
  
          PlainDate iso = PlainDate.from(date); // includes validation
          return CalendarYear.of(iso.getYear());
  
      }
docs: /*[deutsch]
  <p>Konvertiert das angegebene gregorianische Datum zu einem Kalenderjahr. </p>
  
  @param   date    gregorian calendar date (for example {@code PlainDate}
  @return  CalendarYear
  @throws  IllegalArgumentException if given date is invalid
  @since   3.28/4.24