code: public YearMonth minusYears(long yearsToSubtract) {
          return (yearsToSubtract == Long.MIN_VALUE ? plusYears(Long.MAX_VALUE).plusYears(1) : plusYears(-yearsToSubtract));
      }
docs: Returns a copy of this {@code YearMonth} with the specified number of years subtracted.
  <p>
  This instance is immutable and unaffected by this method call.
  
  @param yearsToSubtract  the years to subtract, may be negative
  @return a {@code YearMonth} based on this year-month with the years subtracted, not null
  @throws DateTimeException if the result exceeds the supported range