- [x] I have searched the [issues](https://github.com/apache/dubbo/issues) of this repository and believe that this is not a duplicate.
- [x] 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: 2.7.1
* Operating System version: Windows
* Java version: 1.8

### Steps to reproduce this issue

When I config `TagRouter` like this (in Dubbo admin):

```YAML
enabled: true
force: false
runtime: false
tags:
  - name: tag1
    addresses: null
  - name: tag2
    addresses: null
```

### Actual Result

Then the `java.lang.NullPointerException` was caused

```
java.lang.NullPointerException
	at org.apache.dubbo.rpc.cluster.router.tag.model.TagRouterRule.lambda$init$2(TagRouterRule.java:55)
	at java.util.ArrayList.forEach(ArrayList.java:1257)
	at org.apache.dubbo.rpc.cluster.router.tag.model.TagRouterRule.init(TagRouterRule.java:53)
	at org.apache.dubbo.rpc.cluster.router.tag.model.TagRuleParser.parse(TagRuleParser.java:42)
```

I think we should add NPE check in `TagRouterRule` or check `addresses ` in Dubbo admin

```java
tags.forEach(tag -> {
    tagnameToAddresses.put(tag.getName(), tag.getAddresses());
   // check  tag.getAddresses() not null
    tag.getAddresses().forEach(addr -> {
        List<String> tagNames = addressToTagnames.computeIfAbsent(addr, k -> new ArrayList<>());
        tagNames.add(tag.getName());
    });
});
```


}
    @Test
    public void normalTagRuleTest() {
        String serviceStr = "---\n" +
                "force: false\n" +
                "runtime: true\n" +
                "enabled: false\n" +
                "priority: 1\n" +
                "key: demo-provider\n" +
                "tags:\n" +
                "  - name: tag1\n" +
                "    addresses: [\"30.5.120.37:20881\"]\n" +
                "  - name: tag2\n" +
                "    addresses: [\"30.5.120.37:20880\"]\n" +
                "...";
        try {
            String servicePath = "/dubbo/config/demo-provider/tag-router";
            if (client.checkExists().forPath(servicePath) == null) {
                client.create().creatingParentsIfNeeded().forPath(servicePath);
            }
            setData(servicePath, serviceStr);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    private void setData(String path, String data) throws Exception {
        client.setData().forPath(path, data.getBytes());
    }
}