Loading attached fxml file throws the following assertion error :

Exception in thread "JavaFX Application Thread" java.lang.AssertionError
at com.oracle.javafx.scenebuilder.kit.fxom.FXOMLoader.beginInstanceDeclarationElement(FXOMLoader.java:119)
at javafx.fxml.FXMLLoader.createElement(FXMLLoader.java:2772)
at javafx.fxml.FXMLLoader.processStartElement(FXMLLoader.java:2714)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2521)
at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2419)
at com.oracle.javafx.scenebuilder.kit.fxom.FXOMLoader.load(FXOMLoader.java:88)
at com.oracle.javafx.scenebuilder.kit.fxom.FXOMDocument.<init>(FXOMDocument.java:75)
at com.oracle.javafx.scenebuilder.kit.editor.EditorController.updateFxomDocument(EditorController.java:1716)
at com.oracle.javafx.scenebuilder.kit.editor.EditorController.setFxmlTextAndLocation(EditorController.java:545)
at com.oracle.javafx.scenebuilder.app.DocumentWindowController.loadFromFile(DocumentWindowController.java:347)
at com.oracle.javafx.scenebuilder.app.SceneBuilderApp.performOpenFiles(SceneBuilderApp.java:432)
at com.oracle.javafx.scenebuilder.app.SceneBuilderApp.performOpenRecent(SceneBuilderApp.java:157)
at com.oracle.javafx.scenebuilder.app.menubar.MenuBarController$16.handle(MenuBarController.java:1036)
at com.oracle.javafx.scenebuilder.app.menubar.MenuBarController$16.handle(MenuBarController.java:1031)
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)