code: public static Period rightShift(YearMonth self, YearMonth other) {
          return Period.between(self.atDay(1), other.atDay(1));
      }
docs: Returns a {@link java.time.Period} of time between the first day of this year/month (inclusive) and the
  given {@link java.time.YearMonth} (exclusive).
  
  @param self  a YearMonth
  @param other another YearMonth
  @return a Period
  @since 2.5.0