code: function() {
        return ICAL.Period.fromData({
          start: this.start ? this.start.clone() : null,
          end: this.end ? this.end.clone() : null,
          duration: this.duration ? this.duration.clone() : null
        });
      }
docs: Returns a clone of the duration object.
  
  @return {ICAL.Period}      The cloned object