NullPointException occurred when ClusterServer shutdown and then startup

[all4you]

Issue Description

[bug1] I created one ClusterServer and two ClusterClients, the clients are connected to the server. I shutdown the server and then startup, and then the NPE occurred.

[bug2] The total connection count is also not correct, the count should be 2 but it is 1 shown in the TokenServer list page. While the state of two cluster clients are connected that i can see it in TokenClient list page.

Describe what happened (or what feature you want)

The stack error msg is blow:
Sat Jan 26 21:01:26 CST 2019 sun.misc.Launcher$AppClassLoader@18b4aac2 JM.Log:INFO Log root path: /Users/wanghui/logs/
Sat Jan 26 21:01:26 CST 2019 sun.misc.Launcher$AppClassLoader@18b4aac2 JM.Log:INFO Set nacos log path: /Users/wanghui/logs/nacos
21:01:26.764 [main] INFO com.alibaba.nacos.client.identify.CredentialWatcher - [appA] [] [] No credential found
21:01:27.450 [nioEventLoopGroup-2-1] INFO io.netty.handler.logging.LoggingHandler - [id: 0xf468a88d] REGISTERED
21:01:27.451 [nioEventLoopGroup-2-1] INFO io.netty.handler.logging.LoggingHandler - [id: 0xf468a88d] BIND: 0.0.0.0/0.0.0.0:11111
21:01:27.459 [nioEventLoopGroup-2-1] INFO io.netty.handler.logging.LoggingHandler - [id: 0xf468a88d, L:/0:0:0:0:0:0:0:0:11111] ACTIVE
21:01:28.711 [nioEventLoopGroup-2-1] INFO io.netty.handler.logging.LoggingHandler - [id: 0xf468a88d, L:/0:0:0:0:0:0:0:0:11111] READ: [id: 0xe2e5b58d, L:/192.168.0.104:11111 - R:/192.168.0.104:64840]
21:01:28.712 [nioEventLoopGroup-2-1] WARN io.netty.bootstrap.ServerBootstrap - Unknown channel option 'SO_TIMEOUT' for channel '[id: 0xe2e5b58d, L:/192.168.0.104:11111 - R:/192.168.0.104:64840]'
21:01:28.712 [nioEventLoopGroup-2-1] INFO io.netty.handler.logging.LoggingHandler - [id: 0xf468a88d, L:/0:0:0:0:0:0:0:0:11111] READ COMPLETE
21:01:28.717 [nioEventLoopGroup-2-1] INFO io.netty.handler.logging.LoggingHandler - [id: 0xf468a88d, L:/0:0:0:0:0:0:0:0:11111] READ: [id: 0x9f7bb1af, L:/192.168.0.104:11111 - R:/192.168.0.104:64841]
21:01:28.717 [nioEventLoopGroup-2-1] WARN io.netty.bootstrap.ServerBootstrap - Unknown channel option 'SO_TIMEOUT' for channel '[id: 0x9f7bb1af, L:/192.168.0.104:11111 - R:/192.168.0.104:64841]'
21:01:28.717 [nioEventLoopGroup-2-1] INFO io.netty.handler.logging.LoggingHandler - [id: 0xf468a88d, L:/0:0:0:0:0:0:0:0:11111] READ COMPLETE
21:01:28.742 [nioEventLoopGroup-3-1] WARN io.netty.channel.DefaultChannelPipeline - An exceptionCaught() event was fired, and it reached at the tail of the pipeline. It usually means the last handler in the pipeline did not handle the exception.
java.lang.NullPointerException: null
at com.alibaba.csp.sentinel.cluster.server.connection.ConnectionManager.addConnection(ConnectionManager.java:97) ~[sentinel-cluster-server-default-1.4.1.jar:?]
at com.alibaba.csp.sentinel.cluster.server.handler.TokenServerHandler.handlePingRequest(TokenServerHandler.java:103) ~[sentinel-cluster-server-default-1.4.1.jar:?]
at com.alibaba.csp.sentinel.cluster.server.handler.TokenServerHandler.channelRead(TokenServerHandler.java:69) ~[sentinel-cluster-server-default-1.4.1.jar:?]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362) [netty-transport-4.1.31.Final.jar:4.1.31.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348) [netty-transport-4.1.31.Final.jar:4.1.31.Final]
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340) [netty-transport-4.1.31.Final.jar:4.1.31.Final]
at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:323) [netty-codec-4.1.31.Final.jar:4.1.31.Final]
at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:297) [netty-codec-4.1.31.Final.jar:4.1.31.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362) [netty-transport-4.1.31.Final.jar:4.1.31.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348) [netty-transport-4.1.31.Final.jar:4.1.31.Final]
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340) [netty-transport-4.1.31.Final.jar:4.1.31.Final]
at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:323) [netty-codec-4.1.31.Final.jar:4.1.31.Final]
at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:297) [netty-codec-4.1.31.Final.jar:4.1.31.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362) [netty-transport-4.1.31.Final.jar:4.1.31.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348) [netty-transport-4.1.31.Final.jar:4.1.31.Final]
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340) [netty-transport-4.1.31.Final.jar:4.1.31.Final]
at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1434) [netty-transport-4.1.31.Final.jar:4.1.31.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362) [netty-transport-4.1.31.Final.jar:4.1.31.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348) [netty-transport-4.1.31.Final.jar:4.1.31.Final]
at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:965) [netty-transport-4.1.31.Final.jar:4.1.31.Final]
at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:163) [netty-transport-4.1.31.Final.jar:4.1.31.Final]
at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:648) [netty-transport-4.1.31.Final.jar:4.1.31.Final]
at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:583) [netty-transport-4.1.31.Final.jar:4.1.31.Final]
at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:500) [netty-transport-4.1.31.Final.jar:4.1.31.Final]
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:462) [netty-transport-4.1.31.Final.jar:4.1.31.Final]
at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:897) [netty-common-4.1.31.Final.jar:4.1.31.Final]
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) [netty-common-4.1.31.Final.jar:4.1.31.Final]
at java.lang.Thread.run(Thread.java:748) [?:1.8.0_152]

Describe what you expected to happen

No NPE should be thrown

How to reproduce it (as minimally and precisely as possible)

1. start a token server
2. start two token client and connect the token server
3. shutdown the token server
   4.restart the token server

Tell us your environment

OS:
Darwin 18.2.0 Darwin Kernel Version 18.2.0: Mon Nov 12 20:24:46 PST 2018; root:xnu-4903.231.4~2/RELEASE_X86_64 x86_64
JDK:
java version "1.8.0_152"
Java(TM) SE Runtime Environment (build 1.8.0_152-b16)
Java HotSpot(TM) 64-Bit Server VM (build 25.152-b16, mixed mode)

Anything else we need to know?

None

[zhoushuai1119]

我启动token-server也是报这个错误，请问一下是怎么解决的嘛？