@Override
    public Set<String> getCriticalExtensionOIDs() {
        String[] critOids =
                NativeCrypto.get_X509_CRL_ext_oids(mContext, this, NativeCrypto.EXTENSION_TYPE_CRITICAL);

        /*
         * This API has a special case that if there are no extensions, we
         * should return null. So if we have no critical extensions, we'll check
         * non-critical extensions.
         */
        if ((critOids.length == 0)
                && (NativeCrypto.get_X509_CRL_ext_oids(mContext, this,
                        NativeCrypto.EXTENSION_TYPE_NON_CRITICAL).length == 0)) {
            return null;
        }

        return new HashSet<>(Arrays.asList(critOids));
    }
An implementation of {@link X509CRL} based on BoringSSL.
common/src/main/java/org/conscrypt/OpenSSLX509CRL.java