code: public static MutablePeriod parse(String str, PeriodFormatter formatter) {
          return formatter.parsePeriod(str).toMutablePeriod();
      }
docs: Parses a {@code MutablePeriod} from the specified string using a formatter.
  
  @param str  the string to parse, not null
  @param formatter  the formatter to use, not null
  @since 2.0