code: public static YearMonth randomYearMonthAfter(YearMonth after) {
      checkArgument(after != null, "After must be non-null");
      LocalDate start = after.plus(1, MONTHS).atDay(1);
      LocalDate localDate = randomLocalDateAfter(start);
      return YearMonth.of(localDate.getYear(), localDate.getMonth());
    }
docs: Returns a random {@link YearMonth} that is after the given {@link YearMonth}.
  
  @param after the value that returned {@link YearMonth} must be after
  @return the random {@link YearMonth}
  @throws IllegalArgumentException if after is null or if after is equal to or after {@link
  RandomDateUtils#MAX_INSTANT}