[JavaFX Application Thread] ERROR org.jabref.FallbackExceptionHandler - Uncaught exception occurred in Thread[JavaFX Application Thread,5,main]
java.lang.NullPointerException: null
  at org.jabref.gui.preferences.AppearancePrefsTab.<init>(AppearancePrefsTab.java:56) ~[JabRef--master--latest.jar:?]
  at org.jabref.gui.preferences.PreferencesDialog.<init>(PreferencesDialog.java:91) ~[JabRef--master--latest.jar:?]
  at org.jabref.gui.actions.ShowPreferencesAction.execute(ShowPreferencesAction.java:15) ~[JabRef--master--latest.jar:?]
  at org.jabref.gui.actions.JabRefAction.lambda$new$899(JabRefAction.java:29) ~[JabRef--master--latest.jar:?]
  at org.controlsfx.control.action.Action.handle(Action.java:419) ~[JabRef--master--latest.jar:?]
  at org.controlsfx.control.action.Action.handle(Action.java:64) ~[JabRef--master--latest.jar:?]
  at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86) ~[jfxrt.jar:?]
  at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238) ~[jfxrt.jar:?]
  at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191) ~[jfxrt.jar:?]
  at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58) ~[jfxrt.jar:?]
  at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114) ~[jfxrt.jar:?]
  at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74) ~[jfxrt.jar:?]
  at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49) ~[jfxrt.jar:?]
  at javafx.event.Event.fireEvent(Event.java:198) ~[jfxrt.jar:?]
  at javafx.scene.control.MenuItem.fire(MenuItem.java:462) ~[jfxrt.jar:?]
  at com.sun.javafx.scene.control.skin.ContextMenuContent$MenuItemContainer.doSelect(ContextMenuContent.java:1405) ~[jfxrt.jar:?]
  at com.sun.javafx.scene.control.skin.ContextMenuContent$MenuItemContainer.lambda$createChildren$6(ContextMenuContent.java:1358) ~[jfxrt.jar:?]
  at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218) ~[jfxrt.jar:?]
  at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80) ~[jfxrt.jar:?]
  at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238) ~[jfxrt.jar:?]
  at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191) ~[jfxrt.jar:?]
  at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59) ~[jfxrt.jar:?]
  at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58) ~[jfxrt.jar:?]
  at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114) ~[jfxrt.jar:?]
  at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56) ~[jfxrt.jar:?]
  at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114) ~[jfxrt.jar:?]
  at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56) ~[jfxrt.jar:?]
  at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114) ~[jfxrt.jar:?]
  at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56) ~[jfxrt.jar:?]
  at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114) ~[jfxrt.jar:?]
  at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74) ~[jfxrt.jar:?]
  at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54) ~[jfxrt.jar:?]
  at javafx.event.Event.fireEvent(Event.java:198) ~[jfxrt.jar:?]
  at javafx.scene.Scene$MouseHandler.process(Scene.java:3757) ~[jfxrt.jar:?]
  at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485) ~[jfxrt.jar:?]
  at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762) ~[jfxrt.jar:?]
  at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494) ~[jfxrt.jar:?]
  at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:394) ~[jfxrt.jar:?]
  at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295) ~[jfxrt.jar:?]
  at java.security.AccessController.doPrivileged(Native Method) ~[?:1.8.0_181]
  at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:432) ~[jfxrt.jar:?]
  at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389) ~[jfxrt.jar:?]
  at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:431) ~[jfxrt.jar:?]
  at com.sun.glass.ui.View.handleMouseEvent(View.java:555) ~[jfxrt.jar:?]
  at com.sun.glass.ui.View.notifyMouse(View.java:937) ~[jfxrt.jar:?]
  at com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method) ~[jfxrt.jar:?]
  at com.sun.glass.ui.gtk.GtkApplication.lambda$null$5(GtkApplication.java:139) ~[jfxrt.jar:?]
  at java.lang.Thread.run(Thread.java:748) [?:1.8.0_181]