- [ ] 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: 2.7.5
* Zookeeper version: 3.4.14
* Operating System version: macos
* Java version: 1.8

### Steps to reproduce this issue

1. 按官方文档搭建provider，两种方式：annotation/xml
2. 分别配置

```xml
    <dubbo:metadata-report address="zookeeper://127.0.0.1:2181"/>
```

```java
        @Bean
        public MetadataReportConfig metadataReportConfig() {
            MetadataReportConfig metadataReportConfig = new MetadataReportConfig();
            metadataReportConfig.setAddress("zookeeper://127.0.0.1:2181");
            return metadataReportConfig;
        }
```

3. 应用正常启动
4. Consumer端正常调用
4. 观察Zookeeper节点数据，元数据节点/dubbo/metadata 未创建

### Expected Result
元数据正常上报

### Actual Result

元数据节点在Zookeeper上未创建，元数据未上报

> 将dubbo版本号更改为2.7.4.1、2.7.3，代码或配置未改动，元数据正常上报

* A {@link ProxyFactory} implementation that will generate a exported service proxy,the JavassistProxyFactory is its
     * default implementation
     */
    private static final ProxyFactory PROXY_FACTORY = ExtensionLoader.getExtensionLoader(ProxyFactory.class).getAdaptiveExtension();
    /**
     * Whether the provider has been exported
     */
    private transient volatile boolean exported;
    /**
     * The flag whether a service has unexported ,if the method unexported is invoked, the value is true
     */
    private transient volatile boolean unexported;
    private DubboBootstrap bootstrap;
    /**
     * The exported services
     */
    private final List<Exporter<?>> exporters = new ArrayList<Exporter<?>>();
    public ServiceConfig() {
    }
    public ServiceConfig(Service service) {
        super(service);
    }
    @Parameter(excluded = true)
    public boolean isExported() {
        return exported;
    }
    @Parameter(excluded = true)
    public boolean isUnexported() {
        return unexported;
    }