code: public Period minusYears(long yearsToSubtract) {
          return (yearsToSubtract == Long.MIN_VALUE ? plusYears(Long.MAX_VALUE).plusYears(1) : plusYears(-yearsToSubtract));
      }
docs: Returns a copy of this period with the specified years subtracted.
  <p>
  This subtracts the amount from the years unit in a copy of this period.
  The months and days units are unaffected.
  For example, "1 year, 6 months and 3 days" minus 2 years returns "-1 years, 6 months and 3 days".
  <p>
  This instance is immutable and unaffected by this method call.
  
  @param yearsToSubtract  the years to subtract, positive or negative
  @return a {@code Period} based on this period with the specified years subtracted, not null
  @throws ArithmeticException if numeric overflow occurs