Open attached FXML
Select the Button which is a graphic of the Tab
Choose Arrange > Wrap In - BUG - as soon as you hover over the Wrap In menu item the below Exception occurs. Note, this also happens if you try and choose Wrap in from contextual menu. Also note that this has very odd side effects when running from the nightly (the node can disappear etc).

SEVERE: An exception was thrown:
java.lang.AssertionError
at com.oracle.javafx.scenebuilder.kit.editor.job.wrap.AbstractWrapInJob.makeSubJobs(AbstractWrapInJob.java:198)
at com.oracle.javafx.scenebuilder.kit.editor.job.BatchDocumentJob.getSubJobs(BatchDocumentJob.java:56)
at com.oracle.javafx.scenebuilder.kit.editor.job.BatchDocumentJob.isExecutable(BatchDocumentJob.java:64)
at com.oracle.javafx.scenebuilder.kit.editor.EditorController.canPerformWrap(EditorController.java:1685)
at com.oracle.javafx.scenebuilder.kit.editor.EditorController.canPerformEditAction(EditorController.java:1302)
at com.oracle.javafx.scenebuilder.app.menubar.MenuBarController$EditActionController.canPerform(MenuBarController.java:1555)
at com.oracle.javafx.scenebuilder.app.menubar.MenuBarController.handleOnMenuValidation(MenuBarController.java:1068)
at com.oracle.javafx.scenebuilder.app.menubar.MenuBarController.lambda$new$16(MenuBarController.java:1057)
at com.oracle.javafx.scenebuilder.app.menubar.MenuBarController$$Lambda$74/1808118780.handle(Unknown Source)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.event.Event.fireEvent(Event.java:198)
at com.sun.javafx.scene.control.GlobalMenuAdapter$MenuItemAdapter.fireValidation(GlobalMenuAdapter.java:187)
at com.sun.javafx.tk.quantum.GlassSystemMenu$1.validate(GlassSystemMenu.java:243)