`Exception in thread "AWT-EventQueue-1" java.lang.IllegalArgumentException: missing event subscriber for an annotated method. Is net.sf.jabref.logic.autosaveandbackup.BackupManager@5fa93a28 registered?
at com.google.common.eventbus.SubscriberRegistry.unregister(SubscriberRegistry.java:111)
at com.google.common.eventbus.EventBus.unregister(EventBus.java:201)
at net.sf.jabref.model.database.BibDatabase.unregisterListener(BibDatabase.java:579)
at net.sf.jabref.logic.autosaveandbackup.BackupManager.shutdown(BackupManager.java:94)
at net.sf.jabref.logic.autosaveandbackup.BackupManager.lambda$shutdown$1(BackupManager.java:141)
at java.util.Optional.ifPresent(Optional.java:159)
at net.sf.jabref.logic.autosaveandbackup.BackupManager.shutdown(BackupManager.java:140)
at net.sf.jabref.gui.JabRefFrame.quit(JabRefFrame.java:856)
at net.sf.jabref.gui.JabRefFrame$CloseAction.actionPerformed(JabRefFrame.java:1772)
at net.sf.jabref.gui.JabRefFrame$2.windowClosing(JabRefFrame.java:600)
at java.awt.AWTEventMulticaster.windowClosing(AWTEventMulticaster.java:349)
at java.awt.AWTEventMulticaster.windowClosing(AWTEventMulticaster.java:349)
at java.awt.AWTEventMulticaster.windowClosing(AWTEventMulticaster.java:349)
at java.awt.AWTEventMulticaster.windowClosing(AWTEventMulticaster.java:349)
at java.awt.Window.processWindowEvent(Window.java:2054)
at javax.swing.JFrame.processWindowEvent(JFrame.java:305)
at java.awt.Window.processEvent(Window.java:2013)
at java.awt.Component.dispatchEventImpl(Component.java:4889)
at java.awt.Container.dispatchEventImpl(Container.java:2294)
at java.awt.Window.dispatchEventImpl(Window.java:2746)
at java.awt.Component.dispatchEvent(Component.java:4711)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
at java.awt.EventQueue.access$500(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:709)
at java.awt.EventQueue$3.run(EventQueue.java:703)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.awt.EventQueue$4.run(EventQueue.java:731)
at java.awt.EventQueue$4.run(EventQueue.java:729)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
at org.GNOME.Accessibility.AtkWrapper$5.dispatchEvent(AtkWrapper.java:700)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)