code: public long getInstantMillis(Object object, Chronology chrono) {
          Calendar calendar = (Calendar) object;
          return calendar.getTime().getTime();
      }
docs: Gets the millis, which is the Calendar millis value.
  
  @param object  the Calendar to convert, must not be null
  @param chrono  the chronology result from getChronology, non-null
  @return the millisecond value
  @throws NullPointerException if the object is null
  @throws ClassCastException if the object is an invalid type