java.lang.IllegalArgumentException: No element of a node selection may be null.
	at org.openide.explorer.ExplorerManager$1AtomicSetSelectedNodes.checkArgumentIsValid(ExplorerManager.java:206)
	at org.openide.explorer.ExplorerManager$1AtomicSetSelectedNodes.run(ExplorerManager.java:267)
	at org.openide.util.Mutex.readAccess(Mutex.java:296)
	at org.openide.explorer.ExplorerManager.setSelectedNodes(ExplorerManager.java:274)
	at org.netbeans.modules.form.FormDesigner$3.propertyChange(FormDesigner.java:252)
	at java.beans.PropertyChangeSupport.firePropertyChange(PropertyChangeSupport.java:339)
	at java.beans.PropertyChangeSupport.firePropertyChange(PropertyChangeSupport.java:347)
	at java.beans.PropertyChangeSupport.firePropertyChange(PropertyChangeSupport.java:276)
	at java.awt.Component.firePropertyChange(Component.java:7865)
	at org.openide.windows.TopComponent.setActivatedNodes(TopComponent.java:291)
	at org.netbeans.modules.form.FormDesigner.updateComponentInspector(FormDesigner.java:1323)
	at org.netbeans.modules.form.FormDesigner.setSelectedComponent(FormDesigner.java:879)
	at org.netbeans.modules.form.HandleLayer.selectComponent(HandleLayer.java:626)
	at org.netbeans.modules.form.HandleLayer.mousePressed(HandleLayer.java:1549)
	at java.awt.Component.processMouseEvent(Component.java:6035)
	at javax.swing.JComponent.processMouseEvent(JComponent.java:3260)
	at java.awt.Component.processEvent(Component.java:5803)
	at java.awt.Container.processEvent(Container.java:2058)
	at java.awt.Component.dispatchEventImpl(Component.java:4410)
	at java.awt.Container.dispatchEventImpl(Container.java:2116)
	at java.awt.Component.dispatchEvent(Component.java:4240)
	at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4322)
	at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3983)
	at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3916)
	at java.awt.Container.dispatchEventImpl(Container.java:2102)
	at java.awt.Window.dispatchEventImpl(Window.java:2429)
	at java.awt.Component.dispatchEvent(Component.java:4240)
[catch] at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
	at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
	at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)