#vulnerable code 
                                private static boolean checkRpkIdentity(String endpoint, Identity clientIdentity, SecurityInfo securityInfo) {
        // Manage RPK authentication
        // ----------------------------------------------------
        PublicKey publicKey = clientIdentity.getRawPublicKey();
        if (publicKey == null || !publicKey.equals(securityInfo.getRawPublicKey())) {
            if (LOG.isDebugEnabled()) {
                LOG.debug("Invalid rpk for client {}: expected \n'{}'\n but was \n'{}'", endpoint,
                        Hex.encodeHexString(securityInfo.getRawPublicKey().getEncoded()),
                        Hex.encodeHexString(publicKey.getEncoded()));
            }
            return false;
        } else {
            LOG.trace("authenticated client '{}' using DTLS RPK", endpoint);
            return true;
        }
    } 
                            #location 9 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                private static boolean checkRpkIdentity(String endpoint, Identity clientIdentity, SecurityInfo securityInfo) {
        // Manage RPK authentication
        // ----------------------------------------------------
        PublicKey publicKey = clientIdentity.getRawPublicKey();
        if (publicKey == null || !publicKey.equals(securityInfo.getRawPublicKey())) {
            if (LOG.isDebugEnabled()) {
                LOG.debug("Invalid rpk for client {}: expected \n'{}'\n but was \n'{}'", endpoint,
                        Hex.encodeHexString(securityInfo.getRawPublicKey().getEncoded()),
                        publicKey != null ? Hex.encodeHexString(publicKey.getEncoded()) : "null");
            }
            return false;
        } else {
            LOG.trace("authenticated client '{}' using DTLS RPK", endpoint);
            return true;
        }
    }