code: public Chronology getChronology(Object object, Chronology chrono) {
          if (chrono != null) {
              return chrono;
          }
          Calendar cal = (Calendar) object;
          DateTimeZone zone = null;
          try {
              zone = DateTimeZone.forTimeZone(cal.getTimeZone());
              
          } catch (IllegalArgumentException ex) {
              zone = DateTimeZone.getDefault();
          }
          return getChronology(cal, zone);
      }
docs: Gets the chronology.
  <p>
  If a chronology is specified then it is used.
  Otherwise, it is the GJChronology if a GregorianCalendar is used,
  BuddhistChronology if a BuddhistCalendar is used or ISOChronology otherwise.
  The time zone is extracted from the calendar if possible, default used if not.
  
  @param object  the Calendar to convert, must not be null
  @param chrono  the chronology to use, null means use Calendar
  @return the chronology, never null
  @throws NullPointerException if the object is null
  @throws ClassCastException if the object is an invalid type