### Environment

* Dubbo version: 2.7.5
* Operating System version: win10 or centos7
* Java version: 1.8.0
* Zookeeper version: 3.5.6

### Steps to reproduce this issue
My previous dubbo service version was 2.7.3. Today, I upgraded to 2.7.5. I found that the metadata can't be displayed all the time. The dubbo service registry in zookeeper, but zookeeper not /dubbo/metadata node path view.  If I switch back to 2.7.3 and 2.7.4.1, it can be displayed. Are there any bugs? I need help~~

xml-config:
`<dubbo:metadata-report address="zookeeper://192.168.11.100:2181?backup=192.168.11.105:2181" />`
```

}
    public String getEnvironment() {
        return environment;
    }
    public void setEnvironment(String environment) {
        if (environment != null) {
            if (!(DEVELOPMENT_ENVIRONMENT.equals(environment)
                    || TEST_ENVIRONMENT.equals(environment)
                    || PRODUCTION_ENVIRONMENT.equals(environment))) {
                throw new IllegalStateException(String.format("Unsupported environment: %s, only support %s/%s/%s, default is %s.",
                        environment,
                        DEVELOPMENT_ENVIRONMENT,
                        TEST_ENVIRONMENT,
                        PRODUCTION_ENVIRONMENT,
                        PRODUCTION_ENVIRONMENT));
            }
        }
        this.environment = environment;
    }
    public RegistryConfig getRegistry() {
        return CollectionUtils.isEmpty(registries) ? null : registries.get(0);
    }
    public void setRegistry(RegistryConfig registry) {
        List<RegistryConfig> registries = new ArrayList<RegistryConfig>(1);
        registries.add(registry);
        this.registries = registries;
    }
    public List<RegistryConfig> getRegistries() {
        return registries;
    }