### Environment

* Dubbo version: dubbo-registry-nacos 2.7.6
* Operating System version: Win10
* Java version: JAVA 8

### Steps to reproduce this issue
1 springboot  yml配置如下： 
registry:
     address: nacos://127.0.0.1:8848
     simplified: true
     group: dubbo-local
  metadata-report:
            address: nacos://127.0.0.1:8848
            group: dubbo-local

2 登陆nacos 1.2.1 控制台发现元数据 group配置生效，但是服务管理下的group依旧是DEFAULT_GROUP。

3 跟了下dubbo-registry-nacos 2.7.6的代码 发现在调用NamingService中 没有传入配置的group参数，使用的默认组参数 
 public void doRegister(URL url) {
        String serviceName = this.getServiceName(url);
        Instance instance = this.createInstance(url);
        this.execute((namingService) -> {
            namingService.registerInstance(serviceName, instance);
        });
    }

Pls. provide [GitHub address] to reproduce this issue.

### Expected Result

What do you expected from the above steps？

### Actual Result

What actually happens?

If there is an exception, please attach the exception trace:

```
Just put your stack trace here!
```

List<String> serviceNames = new ArrayList<>(categories.size());
        for (String category : categories) {
            final String serviceName = getServiceName(url, category);
            serviceNames.add(serviceName);
        }
        return serviceNames;
    }
    private List<URL> toUrlWithEmpty(URL consumerURL, Collection<Instance> instances) {
        List<URL> urls = buildURLs(consumerURL, instances);
        if (urls.size() == 0) {
            URL empty = URLBuilder.from(consumerURL)
                    .setProtocol(EMPTY_PROTOCOL)
                    .addParameter(CATEGORY_KEY, DEFAULT_CATEGORY)
                    .build();
            urls.add(empty);
        }
        return urls;
    }
    private List<URL> buildURLs(URL consumerURL, Collection<Instance> instances) {
        List<URL> urls = new LinkedList<>();
        if (instances != null && !instances.isEmpty()) {
            for (Instance instance : instances) {
                URL url = buildURL(instance);
                if (UrlUtils.isMatch(consumerURL, url)) {
                    urls.add(url);
                }
            }
        }
        return urls;
    }