The nacos implementation of discovery interface ,custom group name is not supported

[JinPengCN]

What happened:

I want to get some registered services,but the program throwed error about: instance list is empty!
invoking like this:

registry.Discovery.GetService(ctx, "myservice")

What you expected to happen:

no error

How to reproduce it (as minimally and precisely as possible):

Just call registryDiscovery.GetService()

Anything else we need to know?:

The nacos implementation of discovery interface use nacos-sdk-go mothed: SelectInstances
source code:
(github.com/nacos-group/nacos-sdk-go/clients/naming_client)

func (sc *NamingClient) SelectInstances(param vo.SelectInstancesParam) ([]model.Instance, error) {
	if len(param.GroupName) == 0 {
		param.GroupName = constant.DEFAULT_GROUP
	}
	service, err := sc.hostReactor.GetServiceInfo(util.GetGroupName(param.ServiceName, param.GroupName), strings.Join(param.Clusters, ","))
	if err != nil {
		return nil, err
	}
	return sc.selectInstances(service, param.HealthyOnly)
}

(kratos/contrib/registry/nacos/v2)

// GetService return the service instances in memory according to the service name.
func (r *Registry) GetService(_ context.Context, serviceName string) ([]*registry.ServiceInstance, error) {
	res, err := r.cli.SelectInstances(vo.SelectInstancesParam{
		ServiceName: serviceName,
		HealthyOnly: true,
	})
	if err != nil {
		return nil, err
	}
	items := make([]*registry.ServiceInstance, 0, len(res))
	for _, in := range res {
		kind := r.opts.kind
		if k, ok := in.Metadata["kind"]; ok {
			kind = k
		}
		items = append(items, &registry.ServiceInstance{
			ID:        in.InstanceId,
			Name:      in.ServiceName,
			Version:   in.Metadata["version"],
			Metadata:  in.Metadata,
			Endpoints: []string{fmt.Sprintf("%s://%s:%d", kind, in.Ip, in.Port)},
		})
	}
	return items, nil
}

if the param.GroupName is empty, value is DEFAULT_GROUP.But the GetService() can`t pass the GroupName.My service group name is customized,so no value obtained.

Environment:

• Kratos version (use kratos -v): v2.1.2
• Go version (use go version): v1.16.0
• OS (e.g: cat /etc/os-release): windows
• Others:
  kratos/contrib/registry/nacos/v2 version is v2.0.0