code: public final Timestamp addMonth(int amount)
      {
          if (amount == 0 && _precision.includes(Precision.MONTH)) return this;
          return addMonthForPrecision(amount, _precision.includes(Precision.MONTH) ? _precision : Precision.MONTH);
      }
docs: Returns a timestamp relative to this one by the given number of months.
  The day field may be adjusted to account for different month length and
  leap days.  For example, adding one month to {@code 2011-01-31}
  results in {@code 2011-02-28}.
  
  @param amount a number of months.