java.lang.NullPointerException
        at org.netbeans.modules.properties.PropertiesOpen.canClose(PropertiesOpen.java:211)
        at org.netbeans.modules.properties.PropertiesOpen$PropertiesCloneableTopComponent.closeLast(PropertiesOpen.java:1315)
        at org.openide.windows.CloneableTopComponent$Ref.unregister(CloneableTopComponent.java:403)
        at org.openide.windows.CloneableTopComponent$Ref.access$300(CloneableTopComponent.java:267)
        at org.openide.windows.CloneableTopComponent.canClose(CloneableTopComponent.java:206)
        at org.netbeans.modules.properties.PropertiesOpen$PropertiesCloneableTopComponent.canClose(PropertiesOpen.java:992)
        at org.netbeans.core.windows.Central.removeModeTopComponent(Central.java:943)
        at org.netbeans.core.windows.Central.userClosedTopComponent(Central.java:1969)
        at org.netbeans.core.windows.view.DefaultView.userClosedTopComponent(DefaultView.java:741)
        at org.netbeans.core.windows.view.ui.TabbedHandler.actionPerformed(TabbedHandler.java:315)
        at org.netbeans.swing.tabcontrol.TabbedContainer.postActionEvent(TabbedContainer.java:692)
        at org.netbeans.swing.tabcontrol.TabbedContainerUI.shouldPerformAction(TabbedContainerUI.java:162)
        at org.netbeans.swing.tabcontrol.plaf.DefaultTabbedContainerUI.access$2700(DefaultTabbedContainerUI.java:109)
        at org.netbeans.swing.tabcontrol.plaf.DefaultTabbedContainerUI$DisplayerActionListener.actionPerformed(DefaultTabbedContainerUI.java:1266)
        at org.netbeans.swing.tabcontrol.TabDisplayer.postActionEvent(TabDisplayer.java:557)
        at org.netbeans.swing.tabcontrol.TabDisplayerUI.shouldPerformAction(TabDisplayerUI.java:185)
        at org.netbeans.swing.tabcontrol.plaf.BasicTabDisplayerUI.access$1500(BasicTabDisplayerUI.java:117)
        at org.netbeans.swing.tabcontrol.plaf.BasicTabDisplayerUI$BasicDisplayerMouseListener.performCommand(BasicTabDisplayerUI.java:723)
        at org.netbeans.swing.tabcontrol.plaf.BasicTabDisplayerUI$BasicDisplayerMouseListener.potentialCommand(BasicTabDisplayerUI.java:708)
        at org.netbeans.swing.tabcontrol.plaf.BasicTabDisplayerUI$BasicDisplayerMouseListener.mouseReleased(BasicTabDisplayerUI.java:756)
        at java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:272)
        at java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:272)
        at java.awt.Component.processMouseEvent(Component.java:6216)
        at javax.swing.JComponent.processMouseEvent(JComponent.java:3265)
        at java.awt.Component.processEvent(Component.java:5981)
        at java.awt.Container.processEvent(Container.java:2041)
        at java.awt.Component.dispatchEventImpl(Component.java:4583)
        at java.awt.Container.dispatchEventImpl(Container.java:2099)
        at java.awt.Component.dispatchEvent(Component.java:4413)
        at java.awt.LightweightDispatcher.retargetMouseEvent(LightweightDispatcher.java:4556)
        at java.awt.LightweightDispatcher.processMouseEvent(LightweightDispatcher.java:4220)
        at java.awt.LightweightDispatcher.dispatchEvent(LightweightDispatcher.java:4150)
        at java.awt.Container.dispatchEventImpl(Container.java:2085)
        at java.awt.Window.dispatchEventImpl(Window.java:2475)
        at java.awt.Component.dispatchEvent(Component.java:4413)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
        at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:104)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)