code: public static ZonedChronology getInstance(Chronology base, DateTimeZone zone) {
          if (base == null) {
              throw new IllegalArgumentException("Must supply a chronology");
          }
          base = base.withUTC();
          if (base == null) {
              throw new IllegalArgumentException("UTC chronology must not be null");
          }
          if (zone == null) {
              throw new IllegalArgumentException("DateTimeZone must not be null");
          }
          return new ZonedChronology(base, zone);
      }
docs: Create a ZonedChronology for any chronology, overriding any time zone it
  may already have.
  
  @param base base chronology to wrap
  @param zone the time zone
  @throws IllegalArgumentException if chronology or time zone is null