Open attached FXML, then select 1 column of the GridPane located under the configuration tab.
You will get :

java.lang.AssertionError
at com.oracle.javafx.scenebuilder.kit.editor.selection.GridSelectionGroup.collectColumnConstraintsInstances(GridSelectionGroup.java:245)
at com.oracle.javafx.scenebuilder.kit.editor.selection.GridSelectionGroup.collectConstraintInstances(GridSelectionGroup.java:106)
at com.oracle.javafx.scenebuilder.kit.editor.panel.inspector.InspectorPanelController$SelectionState.initialize(InspectorPanelController.java:2018)
at com.oracle.javafx.scenebuilder.kit.editor.panel.inspector.InspectorPanelController$SelectionState.<init>(InspectorPanelController.java:2002)
at com.oracle.javafx.scenebuilder.kit.editor.panel.inspector.InspectorPanelController.updateInspector(InspectorPanelController.java:570)
at com.oracle.javafx.scenebuilder.kit.editor.panel.inspector.InspectorPanelController.editorSelectionDidChange(InspectorPanelController.java:488)
at com.oracle.javafx.scenebuilder.kit.editor.panel.util.AbstractPanelController$6.changed(AbstractPanelController.java:250)
at com.oracle.javafx.scenebuilder.kit.editor.panel.util.AbstractPanelController$6.changed(AbstractPanelController.java:245)
at com.sun.javafx.binding.ExpressionHelper$Generic.fireValueChangedEvent(ExpressionHelper.java:347)
at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:80)
at javafx.beans.property.IntegerPropertyBase.fireValueChangedEvent(IntegerPropertyBase.java:106)
at javafx.beans.property.IntegerPropertyBase.markInvalid(IntegerPropertyBase.java:113)
at javafx.beans.property.IntegerPropertyBase.set(IntegerPropertyBase.java:146)
at com.oracle.javafx.scenebuilder.kit.editor.selection.Selection.incrementRevision(Selection.java:532)
at com.oracle.javafx.scenebuilder.kit.editor.selection.Selection.endUpdate(Selection.java:480)
at com.oracle.javafx.scenebuilder.kit.editor.selection.Selection.select(Selection.java:396)
at com.oracle.javafx.scenebuilder.kit.editor.selection.Selection.select(Selection.java:303)
at com.oracle.javafx.scenebuilder.kit.editor.panel.content.gesture.mouse.SelectAndMoveInGridGesture.mousePressed(SelectAndMoveInGridGesture.java:122)
at com.oracle.javafx.scenebuilder.kit.editor.panel.content.gesture.mouse.AbstractMouseDragGesture.start(AbstractMouseDragGesture.java:112)
at com.oracle.javafx.scenebuilder.kit.editor.panel.content.mode.EditModeController.activateGesture(EditModeController.java:955)
at com.oracle.javafx.scenebuilder.kit.editor.panel.content.mode.EditModeController.mousePressedOnPringLayer(EditModeController.java:929)
at com.oracle.javafx.scenebuilder.kit.editor.panel.content.mode.EditModeController.access$800(EditModeController.java:96)
at com.oracle.javafx.scenebuilder.kit.editor.panel.content.mode.EditModeController$9.handle(EditModeController.java:595)
at com.oracle.javafx.scenebuilder.kit.editor.panel.content.mode.EditModeController$9.handle(EditModeController.java:592)
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.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
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.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
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.Scene$MouseHandler.process(Scene.java:3746)
at javafx.scene.Scene$MouseHandler.access$1800(Scene.java:3471)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1695)
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2486)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:314)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:243)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:345)
at com.sun.glass.ui.View.handleMouseEvent(View.java:526)
at com.sun.glass.ui.View.notifyMouse(View.java:898)