code: public LocalDate plusDays(long daysToAdd) {
          if (daysToAdd == 0) {
              return this;
          }
          long mjDay = Math.addExact(toEpochDay(), daysToAdd);
          return LocalDate.ofEpochDay(mjDay);
      }
docs: Returns a copy of this {@code LocalDate} with the specified number of days added.
  <p>
  This method adds the specified amount to the days field incrementing the
  month and year fields as necessary to ensure the result remains valid.
  The result is only invalid if the maximum/minimum year is exceeded.
  <p>
  For example, 2008-12-31 plus one day would result in 2009-01-01.
  <p>
  This instance is immutable and unaffected by this method call.
  
  @param daysToAdd  the days to add, may be negative
  @return a {@code LocalDate} based on this date with the days added, not null
  @throws DateTimeException if the result exceeds the supported date range