code: public static Months ofYears(int years) {
          if (years == 0) {
              return ZERO;
          }
          return new Months(Math.multiplyExact(years, MONTHS_PER_YEAR));
      }
docs: Obtains a {@code Months} representing the number of months
  equivalent to a number of years.
  <p>
  The resulting amount will be month-based, with the number of months
  equal to the number of years multiplied by 12.
  
  @param years  the number of years, positive or negative
  @return the amount with the input years converted to months, not null
  @throws ArithmeticException if numeric overflow occurs