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