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java.lang.NullPointerException: null at java.util.concurrent.ConcurrentHashMap.get(ConcurrentHashMap.java:936)[na:1.8.0_77] at org.springframework.session.web.socket.handler.WebSocketRegistryListener.registerWsSession(WebSocketRegistryListener.java:118)[spring-session-1.2.1.RELEASE.jar:na] at org.springframework.session.web.socket.handler.WebSocketRegistryListener.afterConnectionEstablished(WebSocketRegistryListener.java:86)[spring-session-1.2.1.RELEASE.jar:na] at org.springframework.session.web.socket.handler.WebSocketRegistryListener.onApplicationEvent(WebSocketRegistryListener.java:67)[spring-session-1.2.1.RELEASE.jar:na] at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:166)[spring-context-4.3.2.RELEASE.jar:4.3.2.RELEASE] at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:138)[spring-context-4.3.2.RELEASE.jar:4.3.2.RELEASE] at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:382)[spring-context-4.3.2.RELEASE.jar:4.3.2.RELEASE] at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:336)[spring-context-4.3.2.RELEASE.jar:4.3.2.RELEASE] at org.springframework.session.web.socket.handler.WebSocketConnectHandlerDecoratorFactory$SessionWebSocketHandler.publishEvent(WebSocketConnectHandlerDecoratorFactory.java:84)[spring-session-1.2.1.RELEASE.jar:na] at org.springframework.session.web.socket.handler.WebSocketConnectHandlerDecoratorFactory$SessionWebSocketHandler.afterConnectionEstablished(WebSocketConnectHandlerDecoratorFactory.java:78)[spring-session-1.2.1.RELEASE.jar:na] at org.springframework.web.socket.handler.WebSocketHandlerDecorator.afterConnectionEstablished(WebSocketHandlerDecorator.java:70)[spring-websocket-4.2.4.RELEASE.jar:4.2.4.RELEASE] at org.springframework.web.socket.handler.LoggingWebSocketHandlerDecorator.afterConnectionEstablished(LoggingWebSocketHandlerDecorator.java:48)[spring-websocket-4.2.4.RELEASE.jar:4.2.4.RELEASE] at org.springframework.web.socket.handler.ExceptionWebSocketHandlerDecorator.afterConnectionEstablished(ExceptionWebSocketHandlerDecorator.java:48)[spring-websocket-4.2.4.RELEASE.jar:4.2.4.RELEASE] at org.springframework.web.socket.sockjs.transport.session.AbstractSockJsSession.delegateConnectionEstablished(AbstractSockJsSession.java:374)[spring-websocket-4.2.4.RELEASE.jar:4.2.4.RELEASE] at org.springframework.web.socket.sockjs.transport.session.WebSocketServerSockJsSession.initializeDelegateSession(WebSocketServerSockJsSession.java:159)[spring-websocket-4.2.4.RELEASE.jar:4.2.4.RELEASE] at org.springframework.web.socket.sockjs.transport.handler.SockJsWebSocketHandler.afterConnectionEstablished(SockJsWebSocketHandler.java:87)[spring-websocket-4.2.4.RELEASE.jar:4.2.4.RELEASE] at org.springframework.web.socket.adapter.standard.StandardWebSocketHandlerAdapter.onOpen(StandardWebSocketHandlerAdapter.java:100)[spring-websocket-4.2.4.RELEASE.jar:4.2.4.RELEASE] at org.apache.tomcat.websocket.server.WsHttpUpgradeHandler.init(WsHttpUpgradeHandler.java:133)[tomcat-embed-websocket-8.5.4.jar:8.5.4] at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:827)[tomcat-embed-core-8.5.4.jar:8.5.4] at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1425)[tomcat-embed-core-8.5.4.jar:8.5.4] at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)[tomcat-embed-core-8.5.4.jar:8.5.4] at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)[na:1.8.0_77] at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)[na:1.8.0_77] at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)[tomcat-embed-core-8.5.4.jar:8.5.4] at java.lang.Thread.run(Thread.java:745)[na:1.8.0_77]