- [ ] 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

public void unexport() {
        if (!exported) {
            return;
        }
        if (unexported) {
            return;
        }
        if (!exporters.isEmpty()) {
            for (Exporter<?> exporter : exporters) {
                try {
                    exporter.unexport();
                } catch (Throwable t) {
                    logger.warn("Unexpected error occured when unexport " + exporter, t);
                }
            }
            exporters.clear();
        }
        unexported = true;
        
        dispatch(new ServiceConfigUnexportedEvent(this));
    }
    public synchronized void export() {
        if (!shouldExport()) {
            return;
        }
        if (bootstrap == null) {
            bootstrap = DubboBootstrap.getInstance();
            bootstrap.init();
        }
        checkAndUpdateSubConfigs();