in dubbo2.7, org.apache.dubbo.samples.generic.GenericProvider execute correctly， but close server throw exception

[cvictory]

java.lang.IllegalStateException: Failed to unregister dubbo://192.168.199.229:20880/org.apache.dubbo.samples.generic.api.IUserService?anyhost=true&application=generic-generic&default.timeout=5000&dubbo=2.0.2&generic=false&interface=org.apache.dubbo.samples.generic.api.IUserService&methods=get&pid=1874&side=provider&specVersion=2.7.0-SNAPSHOT&timestamp=1547385477662 to registry 127.0.0.1:2181, cause: Failed to unregister dubbo://192.168.199.229:20880/org.apache.dubbo.samples.generic.api.IUserService?anyhost=true&application=generic-generic&default.timeout=5000&dubbo=2.0.2&generic=false&interface=org.apache.dubbo.samples.generic.api.IUserService&methods=get&pid=1874&side=provider&specVersion=2.7.0-SNAPSHOT&timestamp=1547385477662 to zookeeper zookeeper://127.0.0.1:2181/org.apache.dubbo.registry.RegistryService?application=generic-generic&dubbo=2.0.2&interface=org.apache.dubbo.registry.RegistryService&pid=1874&specVersion=2.7.0-SNAPSHOT&timestamp=1547385477654, cause: instance must be started before calling this method
	at org.apache.dubbo.registry.support.FailbackRegistry.unregister(FailbackRegistry.java:273)
	at org.apache.dubbo.registry.integration.RegistryProtocol$ExporterChangeableWrapper.unexport(RegistryProtocol.java:637)
	at org.apache.dubbo.registry.integration.RegistryProtocol.destroy(RegistryProtocol.java:408)
	at org.apache.dubbo.qos.protocol.QosProtocolWrapper.destroy(QosProtocolWrapper.java:77)
	at org.apache.dubbo.rpc.protocol.ProtocolListenerWrapper.destroy(ProtocolListenerWrapper.java:75)
	at org.apache.dubbo.rpc.protocol.ProtocolFilterWrapper.destroy(ProtocolFilterWrapper.java:121)
	at org.apache.dubbo.config.DubboShutdownHook.destroyProtocols(DubboShutdownHook.java:103)
	at org.apache.dubbo.config.DubboShutdownHook.doDestroy(DubboShutdownHook.java:91)
	at org.apache.dubbo.config.spring.extension.SpringExtensionFactory$ShutdownHookListener.onApplicationEvent(SpringExtensionFactory.java:114)
	at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:172)
	at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:165)
	at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:139)
	at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:393)
	at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:347)
	at org.springframework.context.support.AbstractApplicationContext.doClose(AbstractApplicationContext.java:991)
	at org.springframework.context.support.AbstractApplicationContext$2.run(AbstractApplicationContext.java:929)
Caused by: org.apache.dubbo.rpc.RpcException: Failed to unregister dubbo://192.168.199.229:20880/org.apache.dubbo.samples.generic.api.IUserService?anyhost=true&application=generic-generic&default.timeout=5000&dubbo=2.0.2&generic=false&interface=org.apache.dubbo.samples.generic.api.IUserService&methods=get&pid=1874&side=provider&specVersion=2.7.0-SNAPSHOT&timestamp=1547385477662 to zookeeper zookeeper://127.0.0.1:2181/org.apache.dubbo.registry.RegistryService?application=generic-generic&dubbo=2.0.2&interface=org.apache.dubbo.registry.RegistryService&pid=1874&specVersion=2.7.0-SNAPSHOT&timestamp=1547385477654, cause: instance must be started before calling this method
	at org.apache.dubbo.registry.zookeeper.ZookeeperRegistry.doUnregister(ZookeeperRegistry.java:125)
	at org.apache.dubbo.registry.support.FailbackRegistry.unregister(FailbackRegistry.java:260)
	... 15 more
Caused by: java.lang.IllegalStateException: instance must be started before calling this method
	at org.apache.dubbo.remoting.zookeeper.curator.CuratorZookeeperClient.delete(CuratorZookeeperClient.java:125)
	at org.apache.dubbo.registry.zookeeper.ZookeeperRegistry.doUnregister(ZookeeperRegistry.java:123)
	... 16 more
Caused by: java.lang.IllegalStateException: instance must be started before calling this method
	at org.apache.curator.shaded.com.google.common.base.Preconditions.checkState(Preconditions.java:444)
	at org.apache.curator.framework.imps.CuratorFrameworkImpl.delete(CuratorFrameworkImpl.java:424)
	at org.apache.dubbo.remoting.zookeeper.curator.CuratorZookeeperClient.delete(CuratorZookeeperClient.java:122)
	... 17 more

[cvictory]

代码的逻辑的入口，参考：org.apache.dubbo.config.DubboShutdownHook#doDestroy。

	at org.apache.dubbo.registry.support.FailbackRegistry.unregister(FailbackRegistry.java:273)
	at org.apache.dubbo.registry.integration.RegistryProtocol$ExporterChangeableWrapper.unexport(RegistryProtocol.java:637)
	at org.apache.dubbo.registry.integration.RegistryProtocol.destroy(RegistryProtocol.java:408)
	at org.apache.dubbo.rpc.protocol.ProtocolFilterWrapper.destroy(ProtocolFilterWrapper.java:121)
	at org.apache.dubbo.qos.protocol.QosProtocolWrapper.destroy(QosProtocolWrapper.java:77)
	at org.apache.dubbo.rpc.protocol.ProtocolListenerWrapper.destroy(ProtocolListenerWrapper.java:75)
	at org.apache.dubbo.config.DubboShutdownHook.destroyProtocols(DubboShutdownHook.java:103)
	at org.apache.dubbo.config.DubboShutdownHook.doDestroy(DubboShutdownHook.java:91)

执行org.apache.dubbo.config.DubboShutdownHook.destroyProtocols之前，已经执行了AbstractRegistryFactory.destroyAll()， 这个方法里已经去执行了zookeeperClient的close方法。参考：org.apache.dubbo.registry.zookeeper.ZookeeperRegistry#destroy

    @Override
    public void destroy() {
        super.destroy();
        try {
            zkClient.close();
        } catch (Exception e) {
            logger.warn("Failed to close zookeeper client " + getUrl() + ", cause: " + e.getMessage(), e);
        }
    }