code: @Override
      public boolean isLeapYear(long prolepticYear) {
          if (prolepticYear <= CUTOVER_YEAR) {
              return JulianChronology.INSTANCE.isLeapYear(prolepticYear);
          }
          return IsoChronology.INSTANCE.isLeapYear(prolepticYear);
      }
docs: Checks if the specified year is a leap year.
  <p>
  The result will return the same as {@link JulianChronology#isLeapYear(long)} for
  year 1752 and earlier, and {@link IsoChronology#isLeapYear(long)} otherwise.
  This method does not validate the year passed in, and only has a
  well-defined result for years in the supported range.
  
  @param prolepticYear  the proleptic-year to check, not validated for range
  @return true if the year is a leap year