unexpected error when unsubscribe service merge2,merge3/org.apache.dubbo.samples.merge.api.MergeService from registry: nacos, dubbo version 3.1.0

[chickenlj]

[03/09/22 06:27:41:041 CST] DubboShutdownHook  WARN integration.DynamicDirectory:  [DUBBO] unexpected error when unsubscribe service merge2,merge3/org.apache.dubbo.samples.merge.api.MergeService from registry: nacos://127.0.0.1:8848/org.apache.dubbo.registry.RegistryService?application=merge-consumer&dubbo=2.0.2&interface=org.apache.dubbo.registry.RegistryService&pid=26840&release=3.1.0, dubbo version: 3.1.0, current host: 30.221.208.119, error code: 1-8. This may be caused by , go to https://dubbo.apache.org/faq/1/8 to find instructions. 
java.lang.IllegalStateException: Failed to unsubscribe consumer://30.221.208.119/org.apache.dubbo.samples.merge.api.MergeService?application=merge-consumer&background=false&category=providers,configurators,routers&dubbo=2.0.2&group=merge2,merge3&interface=org.apache.dubbo.samples.merge.api.MergeService&methods=mergeResult&pid=26840&release=3.1.0&side=consumer&sticky=false&timestamp=1662200561561 to registry 127.0.0.1:8848, cause: null
	at org.apache.dubbo.registry.support.FailbackRegistry.unsubscribe(FailbackRegistry.java:344)
	at org.apache.dubbo.registry.ListenerRegistryWrapper.unsubscribe(ListenerRegistryWrapper.java:136)
	at org.apache.dubbo.registry.integration.DynamicDirectory.destroy(DynamicDirectory.java:309)
	at org.apache.dubbo.registry.integration.RegistryDirectory.destroy(RegistryDirectory.java:135)
	at org.apache.dubbo.rpc.cluster.support.AbstractClusterInvoker.destroy(AbstractClusterInvoker.java:128)
	at org.apache.dubbo.rpc.cluster.support.wrapper.MockClusterInvoker.destroy(MockClusterInvoker.java:87)
	at org.apache.dubbo.registry.client.migration.MigrationInvoker.destroy(MigrationInvoker.java:325)
	at org.apache.dubbo.rpc.proxy.InvokerInvocationHandler.invoke(InvokerInvocationHandler.java:61)
	at org.apache.dubbo.samples.merge.api.MergeServiceDubboProxy1.$destroy(MergeServiceDubboProxy1.java)
	at org.apache.dubbo.config.utils.SimpleReferenceCache.destroyReference(SimpleReferenceCache.java:264)
	at org.apache.dubbo.config.utils.SimpleReferenceCache.lambda$destroyAll$4(SimpleReferenceCache.java:253)
	at java.util.concurrent.ConcurrentHashMap.forEach(ConcurrentHashMap.java:1597)
	at org.apache.dubbo.config.utils.SimpleReferenceCache.destroyAll(SimpleReferenceCache.java:251)
	at org.apache.dubbo.config.deploy.DefaultModuleDeployer.unreferServices(DefaultModuleDeployer.java:402)
	at org.apache.dubbo.config.deploy.DefaultModuleDeployer.postDestroy(DefaultModuleDeployer.java:208)
	at org.apache.dubbo.rpc.model.ModuleModel.onDestroy(ModuleModel.java:108)
	at org.apache.dubbo.rpc.model.ScopeModel.destroy(ScopeModel.java:113)
	at org.apache.dubbo.rpc.model.ApplicationModel.onDestroy(ApplicationModel.java:256)
	at org.apache.dubbo.rpc.model.ScopeModel.destroy(ScopeModel.java:113)
	at org.apache.dubbo.config.DubboShutdownHook.doDestroy(DubboShutdownHook.java:78)
	at org.apache.dubbo.config.DubboShutdownHook.run(DubboShutdownHook.java:73)
Caused by: java.lang.NullPointerException
	at org.apache.dubbo.registry.nacos.NacosRegistry.doUnsubscribe(NacosRegistry.java:280)
	at org.apache.dubbo.registry.support.FailbackRegistry.unsubscribe(FailbackRegistry.java:332)
	... 20 more