code: public static boolean isExpired(final X509CRL crl, final ZonedDateTime reference) {
          return reference.isAfter(DateTimeUtils.zonedDateTimeOf(crl.getNextUpdate()));
      }
docs: Determines whether the given CRL is expired by comparing the nextUpdate field
  with a given date.
  
  @param crl       CRL to examine.
  @param reference Reference date for comparison.
  @return True if reference date is after CRL next update, false otherwise.