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java.lang.NullPointerException at java.util.concurrent.ConcurrentHashMap.get(ConcurrentHashMap.java:936)[?:1.8.0_91] at org.springframework.session.web.socket.handler.WebSocketRegistryListener.registerWsSession(WebSocketRegistryListener.java:118)[spring-session-1.2.0.RELEASE.jar:?] at org.springframework.session.web.socket.handler.WebSocketRegistryListener.afterConnectionEstablished(WebSocketRegistryListener.java:86)[spring-session-1.2.0.RELEASE.jar:?] at org.springframework.session.web.socket.handler.WebSocketRegistryListener.onApplicationEvent(WebSocketRegistryListener.java:67)[spring-session-1.2.0.RELEASE.jar:?] at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:166)[spring-context-4.3.0.RELEASE.jar:4.3.0.RELEASE] at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:138)[spring-context-4.3.0.RELEASE.jar:4.3.0.RELEASE] at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:382)[spring-context-4.3.0.RELEASE.jar:4.3.0.RELEASE] at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:336)[spring-context-4.3.0.RELEASE.jar:4.3.0.RELEASE]