code: public static X509CRLImpl toImpl(X509CRL crl)
              throws CRLException {
          if (crl instanceof X509CRLImpl) {
              return (X509CRLImpl)crl;
          } else {
              return X509Factory.intern(crl);
          }
      }
docs: Utility method to convert an arbitrary instance of X509CRL
  to a X509CRLImpl. Does a cast if possible, otherwise reparses
  the encoding.