code: public Period toPeriod(PeriodType type, Chronology chrono) {
          return new Period(getMillis(), type, chrono);
      }
docs: Converts this duration to a Period instance using the specified period type
  and chronology.
  <p>
  Only precise fields in the period type will be used.
  Exactly which fields are precise depends on the chronology.
  Only the time fields are precise for ISO chronology with a time zone.
  However, ISO UTC also has precise days and weeks.
  <p>
  For more control over the conversion process, you must pair the duration with
  an instant, see {@link #toPeriodFrom(ReadableInstant, PeriodType)} and
  {@link #toPeriodTo(ReadableInstant, PeriodType)}
  
  @param type  the period type to use, null means standard
  @param chrono  the chronology to use, null means ISO default
  @return a Period created using the millisecond duration from this instance