java.lang.NullPointerException: null

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Attempt to invoke virtual method ''int java.lang.Object.hashCode()'' on a null object reference
java.lang.NullPointerException: null
at java.util.concurrent.ConcurrentHashMap.get(ConcurrentHashMap.java:936)
at org.springframework.session.web.socket.handler.WebSocketRegistryListener.registerWsSession(WebSocketRegistryListener.java:118)
at org.springframework.session.web.socket.handler.WebSocketRegistryListener.afterConnectionEstablished(WebSocketRegistryListener.java:86)
at org.springframework.session.web.socket.handler.WebSocketRegistryListener.onApplicationEvent(WebSocketRegistryListener.java:67)
at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:166)
at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:138)
at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:382)
at org.springframework.session.web.socket.handler.WebSocketConnectHandlerDecoratorFactory$SessionWebSocketHandler.publishEvent(WebSocketConnectHandlerDecoratorFactory.java:84)
at org.springframework.session.web.socket.handler.WebSocketConnectHandlerDecoratorFactory$SessionWebSocketHandler.afterConnectionEstablished(WebSocketConnectHandlerDecoratorFactory.java:78)
at org.springframework.web.socket.handler.WebSocketHandlerDecorator.afterConnectionEstablished(WebSocketHandlerDecorator.java:70)
at org.springframework.web.socket.handler.LoggingWebSocketHandlerDecorator.afterConnectionEstablished(LoggingWebSocketHandlerDecorator.java:48)
at org.springframework.web.socket.handler.ExceptionWebSocketHandlerDecorator.afterConnectionEstablished(ExceptionWebSocketHandlerDecorator.java:48)
at org.springframework.web.socket.sockjs.transport.session.AbstractSockJsSession.delegateConnectionEstablished(AbstractSockJsSession.java:374)
at org.springframework.web.socket.sockjs.transport.session.WebSocketServerSockJsSession.initializeDelegateSession(WebSocketServerSockJsSession.java:159)
at org.springframework.web.socket.sockjs.transport.handler.SockJsWebSocketHandler.afterConnectionEstablished(SockJsWebSocketHandler.java:87)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:827)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1425)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.lang.Thread.run(Thread.java:745)

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