code: public DateTime toDateTime(DateTimeZone zone) {
          zone = DateTimeUtils.getZone(zone);
          if (getZone() == zone) {
              return this;
          }
          return super.toDateTime(zone);
      }
docs: Get this object as a DateTime, returning <code>this</code> if possible.
  
  @param zone time zone to apply, or default if null
  @return a DateTime using the same millis