- [ ] I have searched the [issues](https://github.com/apache/dubbo/issues) of this repository and believe that this is not a duplicate.
- [ ] I have checked the [FAQ](https://github.com/apache/dubbo/blob/master/FAQ.md) of this repository and believe that this is not a duplicate.

### Environment

* Dubbo version: 2.7.7-SNAPSHOT
* Operating System version: MacOS
* Java version: OpenJDK 13

### Steps to reproduce this issue

1. Open the dubbo-demo-xml project
2. Modify the registry center both of provider and consumer to Nacos；Open the check switch of consumer
3. Run the provider
4.Run the consumer

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

### Expected Result

The rpc can work properly.

### Actual Result

It fails.

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

```
Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'demoService': FactoryBean threw exception on object creation; nested exception is java.lang.IllegalStateException: Failed to check the status of the service org.apache.dubbo.demo.DemoService. No provider available for the service org.apache.dubbo.demo.DemoService from the url nacos://127.0.0.1:8848/org.apache.dubbo.registry.RegistryService?application=demo-consumer&dubbo=2.0.2&init=false&interface=org.apache.dubbo.demo.DemoService&methods=sayHello,sayHelloAsync&pid=90344&qos.port=33333&register.ip=127.0.0.1&side=consumer&sticky=false&timestamp=1584323664330 to the consumer 127.0.0.1 use dubbo version 
	at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.doGetObjectFromFactoryBean(FactoryBeanRegistrySupport.java:177)
	at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.getObjectFromFactoryBean(FactoryBeanRegistrySupport.java:103)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getObjectForBeanInstance(AbstractBeanFactory.java:1640)
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:254)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202)
	at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1086)
	at org.apache.dubbo.demo.consumer.Application.main(Application.java:33)
Caused by: java.lang.IllegalStateException: Failed to check the status of the service org.apache.dubbo.demo.DemoService. No provider available for the service org.apache.dubbo.demo.DemoService from the url nacos://127.0.0.1:8848/org.apache.dubbo.registry.RegistryService?application=demo-consumer&dubbo=2.0.2&init=false&interface=org.apache.dubbo.demo.DemoService&methods=sayHello,sayHelloAsync&pid=90344&qos.port=33333&register.ip=127.0.0.1&side=consumer&sticky=false&timestamp=1584323664330 to the consumer 127.0.0.1 use dubbo version 
	at org.apache.dubbo.config.ReferenceConfig.createProxy(ReferenceConfig.java:350)
	at org.apache.dubbo.config.ReferenceConfig.init(ReferenceConfig.java:258)
	at org.apache.dubbo.config.ReferenceConfig.get(ReferenceConfig.java:158)
	at org.apache.dubbo.config.spring.ReferenceBean.getObject(ReferenceBean.java:68)
	at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.doGetObjectFromFactoryBean(FactoryBeanRegistrySupport.java:170)
	... 6 more
```
}
        return urls;
    }
    private void subscribeEventListener(String serviceName, final URL url, final NotifyListener listener)
            throws NacosException {
        EventListener eventListener = event -> {
            if (event instanceof NamingEvent) {
                NamingEvent e = (NamingEvent) event;
                notifySubscriber(url, listener, e.getInstances());
            }
        };
        namingService.subscribe(serviceName, eventListener);
    }
    /**
     * Notify the Healthy {@link Instance instances} to subscriber.
     *
     * @param url       {@link URL}
     * @param listener  {@link NotifyListener}
     * @param instances all {@link Instance instances}
     */
    private void notifySubscriber(URL url, NotifyListener listener, Collection<Instance> instances) {
        List<Instance> healthyInstances = new LinkedList<>(instances);
        if (healthyInstances.size() > 0) {
            
            filterHealthyInstances(healthyInstances);
        }
        List<URL> urls = toUrlWithEmpty(url, healthyInstances);
        NacosRegistry.this.notify(url, listener, urls);
    }
    /**