code: public CalendarYear minus(Years<CalendarUnit> years) {
  
          if (years.isEmpty()) {
              return this;
          }
  
          return CalendarYear.of(MathUtils.safeSubtract(this.year, years.getAmount()));
  
      }
docs: /*[deutsch]
  <p>Subtrahiert die angegebenen Jahre von diesem Kalenderjahr. </p>
  
  @param   years       the count of years to be subtracted
  @return  result of subtraction