code: public CalendarYear plus(Years<CalendarUnit> years) {
  
          if (years.isEmpty()) {
              return this;
          }
  
          return CalendarYear.of(MathUtils.safeAdd(this.year, years.getAmount()));
  
      }
docs: /*[deutsch]
  <p>Addiert die angegebenen Jahre zu diesem Kalenderjahr. </p>
  
  @param   years       the count of years to be added
  @return  result of addition