code: public static final Chronology getIntervalChronology(ReadableInstant start, ReadableInstant end) {
          Chronology chrono = null;
          if (start != null) {
              chrono = start.getChronology();
          } else if (end != null) {
              chrono = end.getChronology();
          }
          if (chrono == null) {
              chrono = ISOChronology.getInstance();
          }
          return chrono;
      }
docs: Gets the chronology from the specified instant based interval handling null.
  <p>
  The chronology is obtained from the start if that is not null, or from the
  end if the start is null. The result is additionally checked, and if still
  null then {@link ISOChronology#getInstance()} will be returned.
  
  @param start  the instant to examine and use as the primary source of the chronology
  @param end  the instant to examine and use as the secondary source of the chronology
  @return the chronology, never null