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">


}
    /**
     * Get the key cached in bounds by invoker
     *
     * @param originInvoker
     * @return
     */
    private String getCacheKey(final Invoker<?> originInvoker) {
        URL providerUrl = getProviderUrl(originInvoker);
        String key = providerUrl.removeParameters(DYNAMIC_KEY, ENABLED_KEY).toFullString();
        return key;
    }
    @Override
    @SuppressWarnings("unchecked")
    public <T> Invoker<T> refer(Class<T> type, URL url) throws RpcException {
        url = getRegistryUrl(url);
        Registry registry = getRegistry(url);
        if (RegistryService.class.equals(type)) {
            return proxyFactory.getInvoker((T) registry, type, url);
        }
        
        Map<String, String> qs = (Map<String, String>) url.getAttribute(REFER_KEY);
        String group = qs.get(GROUP_KEY);
        if (StringUtils.isNotEmpty(group)) {
            if ((COMMA_SPLIT_PATTERN.split(group)).length > 1 || "*".equals(group)) {
                return doRefer(Cluster.getCluster(url.getScopeModel(), MergeableCluster.NAME), registry, type, url, qs);
            }
        }
        Cluster cluster = Cluster.getCluster(url.getScopeModel(), qs.get(CLUSTER_KEY));
        return doRefer(cluster, registry, type, url, qs);