code: public static Years<CalendarUnit> ofGregorian(int years) {
  
          return ((years == 0) ? ZERO : (years == 1) ? ONE : new Years<>(years, CalendarUnit.YEARS));
  
      }
docs: /*[deutsch]
  <p>Erh&auml;lt eine Zeitspanne in den angegebenen gregorianischen Jahren. </p>
  
  @param   years       count of gregorian years, maybe negative
  @return  time span in years
  @see     CalendarUnit#YEARS