Dubbo Version: 3.0.10
注册失败，unexport时，subscribeUrl和registerUrl此时为空，需要判断空处理。 
<img width="944" alt="image" src="https://user-images.githubusercontent.com/12670328/200469537-41a4ccb5-adda-4231-9f71-9af9fec2172d.png">


URL urlToRegistry = new ServiceConfigURL(
            parameters.get(PROTOCOL_KEY) == null ? CONSUMER : parameters.get(PROTOCOL_KEY),
            parameters.remove(REGISTER_IP_KEY),
            0,
            getPath(parameters, type),
            parameters
        );
        urlToRegistry = urlToRegistry.setScopeModel(directory.getConsumerUrl().getScopeModel());
        urlToRegistry = urlToRegistry.setServiceModel(directory.getConsumerUrl().getServiceModel());
        if (directory.isShouldRegister()) {
            directory.setRegisteredConsumerUrl(urlToRegistry);
            registry.register(directory.getRegisteredConsumerUrl());
        }
        directory.buildRouterChain(urlToRegistry);
        directory.subscribe(toSubscribeUrl(urlToRegistry));
        return (ClusterInvoker<T>) cluster.join(directory, true);
    }
    public <T> void reRefer(ClusterInvoker<?> invoker, URL newSubscribeUrl) {
        if (!(invoker instanceof MigrationClusterInvoker)) {
            logger.error(REGISTRY_UNSUPPORTED_CATEGORY, "", "", "Only invoker type of MigrationClusterInvoker supports reRefer, current invoker is " + invoker.getClass());
            return;
        }
        MigrationClusterInvoker<?> migrationClusterInvoker = (MigrationClusterInvoker<?>) invoker;
        migrationClusterInvoker.reRefer(newSubscribeUrl);
    }
    public static URL toSubscribeUrl(URL url) {
        return url.addParameter(CATEGORY_KEY, ALL_CATEGORIES);
    }
    protected List<RegistryProtocolListener> findRegistryProtocolListeners(URL url) {
        return ScopeModelUtil.getExtensionLoader(RegistryProtocolListener.class, url.getScopeModel())