code: public LocalDate atYearMonth(YearMonth yearMonth) {
          return yearMonth.atDay(Math.min(day, yearMonth.lengthOfMonth()));
      }
docs: Combines this day-of-month with a year-month to create a {@code LocalDate}.
  <p>
  This returns a {@code LocalDate} formed from this year and the specified year-month.
  <p>
  If this day-of-month is invalid for the year-month then it will be changed
  to the last valid date for the month.
  
  @param yearMonth  the year-month to use, not null
  @return the local date formed from this year and the specified year-month, not null