Import the included file attached.
Then invoke Edit menu.
You will get :

Exception in thread "JavaFX Application Thread" java.lang.AssertionError
at com.oracle.javafx.scenebuilder.kit.fxom.FXOMLoader.endElement(FXOMLoader.java:291)
at javafx.fxml.FXMLLoader.processEndElement(FXMLLoader.java:2842)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2532)
at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2425)
at com.oracle.javafx.scenebuilder.kit.fxom.FXOMLoader.load(FXOMLoader.java:89)
at com.oracle.javafx.scenebuilder.kit.fxom.FXOMDocument.<init>(FXOMDocument.java:80)
at com.oracle.javafx.scenebuilder.kit.fxom.FXOMRefresher.refresh(FXOMRefresher.java:58)
at com.oracle.javafx.scenebuilder.kit.fxom.FXOMDocument.refreshSceneGraph(FXOMDocument.java:267)
at com.oracle.javafx.scenebuilder.kit.fxom.FXOMDocument.endUpdate(FXOMDocument.java:254)
at com.oracle.javafx.scenebuilder.kit.fxom.FXOMNodes.newDocument(FXOMNodes.java:249)
at com.oracle.javafx.scenebuilder.kit.editor.job.DuplicateSelectionJob.makeSubJobs(DuplicateSelectionJob.java:85)
at com.oracle.javafx.scenebuilder.kit.editor.job.v2.CompositeJob.getSubJobs(CompositeJob.java:64)
at com.oracle.javafx.scenebuilder.kit.editor.job.v2.CompositeJob.isExecutable(CompositeJob.java:84)
at com.oracle.javafx.scenebuilder.kit.editor.EditorController.canPerformEditAction(EditorController.java:1061)
at com.oracle.javafx.scenebuilder.app.menubar.MenuBarController$EditActionController.canPerform(MenuBarController.java:1435)
at com.oracle.javafx.scenebuilder.app.menubar.MenuBarController.handleOnMenuValidation(MenuBarController.java:1032)
at com.oracle.javafx.scenebuilder.app.menubar.MenuBarController.access$700(MenuBarController.java:88)
at com.oracle.javafx.scenebuilder.app.menubar.MenuBarController$19.handle(MenuBarController.java:1020)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.event.Event.fireEvent(Event.java:204)
at com.sun.javafx.scene.control.GlobalMenuAdapter$MenuItemAdapter.fireValidation(GlobalMenuAdapter.java:193)
at com.sun.javafx.tk.quantum.GlassSystemMenu$6.validate(GlassSystemMenu.java:243)