- [ ] 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: 2.7.8-SNAPSHOT
* Operating System version: xxx
* Java version: xxx

### Steps to reproduce this issue

1. Do not start zookeeper server, which is used as a metadata center
2. start a provider

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

### Expected Result

The app exit normally

### Actual Result

The app exit with a NPE

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

```
Exception in thread "DubboShutdownHook" java.lang.RuntimeException: java.lang.NullPointerException
	at org.apache.dubbo.common.function.ThrowableAction.execute(ThrowableAction.java:48)
	at org.apache.dubbo.common.lang.ShutdownHookCallbacks.lambda$callback$0(ShutdownHookCallbacks.java:70)
	at java.base/java.lang.Iterable.forEach(Iterable.java:75)
	at org.apache.dubbo.common.lang.ShutdownHookCallbacks.callback(ShutdownHookCallbacks.java:70)
	at org.apache.dubbo.config.DubboShutdownHook.callback(DubboShutdownHook.java:85)
	at org.apache.dubbo.config.DubboShutdownHook.run(DubboShutdownHook.java:73)
Caused by: java.lang.NullPointerException
	at org.apache.dubbo.config.bootstrap.DubboBootstrap.unexportMetadataService(DubboBootstrap.java:1009)
	at org.apache.dubbo.config.bootstrap.DubboBootstrap.destroy(DubboBootstrap.java:1188)
	at org.apache.dubbo.config.bootstrap.DubboBootstrap$1.callback(DubboBootstrap.java:198)
	at org.apache.dubbo.common.function.ThrowableAction.execute(ThrowableAction.java:46)
	... 5 more
```

}
        if (registryConfig.getParameters() != null) {
            metadataReportConfig.getParameters().putAll(registryConfig.getParameters()); 
        }
        metadataReportConfig.getParameters().put(CLIENT_KEY, registryConfig.getClient());
        metadataReportConfig.setGroup(registryConfig.getGroup());
        metadataReportConfig.setAddress(getRegistryCompatibleAddress(registryConfig.getAddress()));
        metadataReportConfig.setUsername(registryConfig.getUsername());
        metadataReportConfig.setPassword(registryConfig.getPassword());
        metadataReportConfig.setTimeout(registryConfig.getTimeout());
        return metadataReportConfig;
    }
    private String getRegistryCompatibleAddress(String registryAddress) {
        String[] addresses = REGISTRY_SPLIT_PATTERN.split(registryAddress);
        if (addresses == null || addresses.length == 0) {
            throw new IllegalStateException("Invalid registry address found.");
        }
        return addresses[0];
    }
    private void loadRemoteConfigs() {
        
        List<RegistryConfig> tmpRegistries = new ArrayList<>();
        Set<String> registryIds = configManager.getRegistryIds();
        registryIds.forEach(id -> {
            if (tmpRegistries.stream().noneMatch(reg -> reg.getId().equals(id))) {
                tmpRegistries.add(configManager.getRegistry(id).orElseGet(() -> {
                    RegistryConfig registryConfig = new RegistryConfig();
                    registryConfig.setId(id);
                    registryConfig.refresh();
                    return registryConfig;