code: public static final Chronology getInstantChronology(ReadableInstant instant) {
          if (instant == null) {
              return ISOChronology.getInstance();
          }
          Chronology chrono = instant.getChronology();
          if (chrono == null) {
              return ISOChronology.getInstance();
          }
          return chrono;
      }
docs: Gets the chronology from the specified instant object handling null.
  <p>
  If the instant object is <code>null</code>, or the instant's chronology is
  <code>null</code>, {@link ISOChronology#getInstance()} will be returned.
  Otherwise, the chronology from the object is returned.
  
  @param instant  the instant to examine, null means ISO in the default zone
  @return the chronology, never null