Loading attached fxml file throws the following assertion error :

Exception in thread "JavaFX Application Thread" java.lang.AssertionError
at com.oracle.javafx.scenebuilder.kit.metadata.util.DesignHierarchyMask.getSubComponentProperty(DesignHierarchyMask.java:641)
at com.oracle.javafx.scenebuilder.kit.metadata.util.DesignHierarchyMask.getSubComponentCount(DesignHierarchyMask.java:526)
at com.oracle.javafx.scenebuilder.kit.editor.panel.hierarchy.AbstractHierarchyPanelController.updateTreeItem(AbstractHierarchyPanelController.java:734)
at com.oracle.javafx.scenebuilder.kit.editor.panel.hierarchy.AbstractHierarchyPanelController.makeTreeItem(AbstractHierarchyPanelController.java:620)
at com.oracle.javafx.scenebuilder.kit.editor.panel.hierarchy.AbstractHierarchyPanelController.updateTreeItems(AbstractHierarchyPanelController.java:687)
at com.oracle.javafx.scenebuilder.kit.editor.panel.hierarchy.treeview.HierarchyTreeViewController.updatePanel(HierarchyTreeViewController.java:98)
at com.oracle.javafx.scenebuilder.kit.editor.panel.hierarchy.AbstractHierarchyPanelController.controllerDidLoadFxml(AbstractHierarchyPanelController.java:531)
at com.oracle.javafx.scenebuilder.kit.editor.panel.util.AbstractFxmlPanelController.makePanel(AbstractFxmlPanelController.java:89)
at com.oracle.javafx.scenebuilder.kit.editor.panel.util.AbstractPanelController.getPanelRoot(AbstractPanelController.java:112)
at com.oracle.javafx.scenebuilder.app.DocumentWindowController.controllerDidLoadFxml(DocumentWindowController.java:813)
at com.oracle.javafx.scenebuilder.kit.editor.panel.util.AbstractFxmlWindowController.makeRoot(AbstractFxmlWindowController.java:99)
at com.oracle.javafx.scenebuilder.kit.editor.panel.util.AbstractWindowController.getRoot(AbstractWindowController.java:83)
at com.oracle.javafx.scenebuilder.kit.editor.panel.util.AbstractWindowController.getScene(AbstractWindowController.java:102)
at com.oracle.javafx.scenebuilder.kit.editor.panel.util.AbstractWindowController.getStage(AbstractWindowController.java:125)
at com.oracle.javafx.scenebuilder.kit.editor.panel.util.AbstractWindowController.openWindow(AbstractWindowController.java:140)
at com.oracle.javafx.scenebuilder.app.SceneBuilderApp.performOpenFiles(SceneBuilderApp.java:433)
at com.oracle.javafx.scenebuilder.app.SceneBuilderApp.performOpenFile(SceneBuilderApp.java:381)
at com.oracle.javafx.scenebuilder.app.SceneBuilderApp.performControlAction(SceneBuilderApp.java:135)
at com.oracle.javafx.scenebuilder.app.menubar.MenuBarController$ApplicationControlActionController.perform(MenuBarController.java:1446)
at com.oracle.javafx.scenebuilder.app.menubar.MenuBarController.handleOnActionMenu(MenuBarController.java:990)
at com.oracle.javafx.scenebuilder.app.menubar.MenuBarController.access$800(MenuBarController.java:89)
at com.oracle.javafx.scenebuilder.app.menubar.MenuBarController$15.handle(MenuBarController.java:983)
at com.oracle.javafx.scenebuilder.app.menubar.MenuBarController$15.handle(MenuBarController.java:979)
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:49)
at javafx.event.Event.fireEvent(Event.java:204)
at javafx.scene.control.MenuItem.fire(MenuItem.java:462)
at com.sun.javafx.scene.control.GlobalMenuAdapter$5.handle(GlobalMenuAdapter.java:158)
at com.sun.javafx.scene.control.GlobalMenuAdapter$5.handle(GlobalMenuAdapter.java:156)
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 javafx.scene.control.MenuItem.fire(MenuItem.java:462)
at com.sun.javafx.tk.quantum.GlassSystemMenu$6.action(GlassSystemMenu.java:234)