public byte[] toBytes() {
        String authzid = authorizationId.isEmpty() ? "" : "a=" + authorizationId;
        String extensions = extensionsMessage();
        if (!extensions.isEmpty())
            extensions = SEPARATOR + extensions;

        String message = String.format("n,%s,%sauth=Bearer %s%s%s%s", authzid,
                SEPARATOR, tokenValue, extensions, SEPARATOR, SEPARATOR);

        return message.getBytes(StandardCharsets.UTF_8);
    }
Return the always non-null extensions

@return the always non-null extensions
clients/src/main/java/org/apache/kafka/common/security/oauthbearer/internals/OAuthBearerClientInitialResponse.java