code: @Override
    public DurationFormatterFactory setPeriodBuilder(PeriodBuilder builder) {
      if (builder != this.builder) {
        this.builder = builder;
        reset();
      }
      return this;
    }
docs: Set the builder used by the factory.  New formatters created
  with this factory will use the given locale.
  
  @param builder the builder to use
  @return this BasicDurationFormatterFactory