code: public static YearQuarter of(int year, Quarter quarter) {
          YEAR.checkValidValue(year);
          Objects.requireNonNull(quarter, "quarter");
          return new YearQuarter(year, quarter);
      }
docs: Obtains an instance of {@code YearQuarter} from a year and quarter.
  
  @param year  the year to represent, from MIN_YEAR to MAX_YEAR
  @param quarter  the quarter-of-year to represent, not null
  @return the year-quarter, not null
  @throws DateTimeException if the year value is invalid