Idempiere 12 session get disconnected

[Aziz Kayoueche]

Hi dear team
I am working with idempiere 12, and  sometimes my session get disconnected and when i checked the log i saw this error, please any help will be appreciated.

java.lang.NullPointerException: Cannot invoke "javax.servlet.http.HttpSession.removeAttribute(String)" because the return value of "org.zkoss.zk.ui.Session.getNativeSession()" is null
at org.zkoss.zk.ui.http.SessionAgent.remove(SessionAgent.java:43)
at org.zkoss.zk.ui.http.SimpleSessionCache.remove(SimpleSessionCache.java:45)
at org.zkoss.zk.ui.impl.AbstractWebApp.sessionDestroyed(AbstractWebApp.java:379)
at org.zkoss.zk.ui.http.WebManager.sessionDestroyed(WebManager.java:527)
at org.zkoss.zk.ui.http.HttpSessionListener23.sessionDestroyed(HttpSessionListener23.java:55)
at org.eclipse.jetty.ee8.nested.SessionHandler$CoreSessionManager.lambda$onSessionDestroyed$1(SessionHandler.java:708)
at org.eclipse.jetty.server.handler.ContextHandler$ScopedContext.run(ContextHandler.java:1524)
at org.eclipse.jetty.server.handler.ContextHandler$ScopedContext.run(ContextHandler.java:1511)
at org.eclipse.jetty.ee8.nested.SessionHandler$CoreSessionManager.onSessionDestroyed(SessionHandler.java:711)
at org.eclipse.jetty.session.AbstractSessionManager.invalidate(AbstractSessionManager.java:816)
at org.eclipse.jetty.session.DefaultSessionIdManager.expireAll(DefaultSessionIdManager.java:417)
at org.eclipse.jetty.session.AbstractSessionManager.scavenge(AbstractSessionManager.java:1146)
at org.eclipse.jetty.session.DefaultSessionIdManager.scavenge(DefaultSessionIdManager.java:452)
at org.eclipse.jetty.session.HouseKeeper.scavenge(HouseKeeper.java:237)
at org.eclipse.jetty.session.HouseKeeper$Runner.run(HouseKeeper.java:53)
at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:539)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:304)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
at java.base/java.lang.Thread.run(Thread.java:840)