Steps to Reproduce

1. run zss app
2. set a shorter session time out, e.g. 30s
3. wait for time out happens

Current Result

15-May-2018 23:36:38.406 SEVERE [ContainerBackgroundProcessor[StandardEngine[Catalina]]] org.zkoss.zk.ui.impl.DesktopImpl.invokeDesktopCleanups Failed to invoke org.zkoss.zss.app.ui.AppCtrl$10@3299c9
java.lang.IllegalStateException: Not in an execution
at org.zkoss.zk.ui.event.impl.EventQueueProviderImpl.lookup(EventQueueProviderImpl.java:58)
at org.zkoss.zkmax.ui.event.impl.EventQueueProviderImpl.lookup(EventQueueProviderImpl.java:57)
at org.zkoss.zk.ui.event.EventQueues.lookup(EventQueues.java:130)
at org.zkoss.zss.model.impl.EventQueueListenerAdaptor.removeEventListener(EventQueueListenerAdaptor.java:64)
at org.zkoss.zss.model.impl.BookImpl.removeEventListener(BookImpl.java:733)
at org.zkoss.zss.ui.Spreadsheet.initBook0(Spreadsheet.java:768)
at org.zkoss.zss.ui.Spreadsheet.setSBook(Spreadsheet.java:679)
at org.zkoss.zss.ui.Spreadsheet.setBook(Spreadsheet.java:6253)
at org.zkoss.zss.app.ui.AppCtrl.doCloseBook(AppCtrl.java:555)
at org.zkoss.zss.app.ui.AppCtrl.doCloseBook(AppCtrl.java:550)
at org.zkoss.zss.app.ui.AppCtrl.access$300(AppCtrl.java:72)
at org.zkoss.zss.app.ui.AppCtrl$10.cleanup(AppCtrl.java:284)
at org.zkoss.zk.ui.impl.DesktopImpl.invokeDesktopCleanups(DesktopImpl.java:1336)
at org.zkoss.zk.ui.impl.SimpleDesktopCache.desktopDestroyed(SimpleDesktopCache.java:142)
at org.zkoss.zk.ui.impl.SimpleDesktopCache.stop(SimpleDesktopCache.java:225)
at org.zkoss.zk.ui.impl.SessionDesktopCacheProvider.sessionDestroyed(SessionDesktopCacheProvider.java:60)
at org.zkoss.zk.ui.impl.AbstractWebApp.sessionDestroyed(AbstractWebApp.java:374)
at org.zkoss.zk.ui.http.WebManager.sessionDestroyed(WebManager.java:456)
at org.zkoss.zk.ui.http.HttpSessionListener23.sessionDestroyed(HttpSessionListener23.java:55)
at org.apache.catalina.session.StandardSession.expire(StandardSession.java:824)
at org.apache.catalina.session.StandardSession.isValid(StandardSession.java:682)
at org.apache.catalina.session.ManagerBase.processExpires(ManagerBase.java:552)
at org.apache.catalina.session.ManagerBase.backgroundProcess(ManagerBase.java:537)
at org.apache.catalina.core.StandardContext.backgroundProcess(StandardContext.java:5572)
at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1388)
at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1392)
at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1392)
at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.run(ContainerBase.java:1360)

Expected Result

no exception