java.lang.NullPointerException
   at org.netbeans.modules.web.browser.ui.HtmlPreviewElement.dettach(HtmlPreviewElement.java:308)
   at org.netbeans.modules.web.browser.ui.HtmlPreviewElement.componentClosed(HtmlPreviewElement.java:194)
   at org.netbeans.core.multiview.MultiViewPeer.peerComponentClosed(MultiViewPeer.java:328)
   at org.netbeans.core.multiview.MultiViewCloneableTopComponent.componentClosed(MultiViewCloneableTopComponent.java:124)
   at org.openide.windows.WindowManager.componentCloseNotify(WindowManager.java:322)
   at org.netbeans.core.windows.WindowManagerImpl.notifyTopComponentClosed(WindowManagerImpl.java:1156)
   at org.netbeans.core.windows.Central.removeModeTopComponent(Central.java:1025)
   at org.netbeans.core.windows.Central.userClosedTopComponent(Central.java:2037)
   at org.netbeans.core.windows.view.DefaultView.userClosedTopComponent(DefaultView.java:794)
   at org.netbeans.core.windows.view.ui.TabbedHandler.actionPerformed(TabbedHandler.java:337)
   at org.netbeans.swing.tabcontrol.TabbedContainer.postActionEvent(TabbedContainer.java:730)
   at org.netbeans.swing.tabcontrol.TabbedContainerUI.shouldPerformAction(TabbedContainerUI.java:165)
   at org.netbeans.swing.tabcontrol.plaf.DefaultTabbedContainerUI.access$2700(DefaultTabbedContainerUI.java:112)
   at org.netbeans.swing.tabcontrol.plaf.DefaultTabbedContainerUI$DisplayerActionListener.actionPerformed(DefaultTabbedContainerUI.java:1286)
   at org.netbeans.swing.tabcontrol.TabDisplayer.postActionEvent(TabDisplayer.java:612)
   at org.netbeans.swing.tabcontrol.TabDisplayerUI.shouldPerformAction(TabDisplayerUI.java:193)
   at org.netbeans.swing.tabcontrol.plaf.BasicTabDisplayerUI.access$1700(BasicTabDisplayerUI.java:121)
   at org.netbeans.swing.tabcontrol.plaf.BasicTabDisplayerUI$BasicDisplayerMouseListener.performCommand(BasicTabDisplayerUI.java:782)
   at org.netbeans.swing.tabcontrol.plaf.BasicTabDisplayerUI$BasicDisplayerMouseListener.potentialCommand(BasicTabDisplayerUI.java:767)
   at org.netbeans.swing.tabcontrol.plaf.BasicTabDisplayerUI$BasicDisplayerMouseListener.mouseReleased(BasicTabDisplayerUI.java:816)
   at java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:289)
   at java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:289)
   at java.awt.Component.processMouseEvent(Component.java:6505)
   at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
   at java.awt.Component.processEvent(Component.java:6270)
   at java.awt.Container.processEvent(Container.java:2229)
   at java.awt.Component.dispatchEventImpl(Component.java:4861)
   at java.awt.Container.dispatchEventImpl(Container.java:2287)
   at java.awt.Component.dispatchEvent(Component.java:4687)
   at java.awt.LightweightDispatcher.retargetMouseEvent(LightweightDispatcher.java:4832)
   at java.awt.LightweightDispatcher.processMouseEvent(LightweightDispatcher.java:4492)
   at java.awt.LightweightDispatcher.dispatchEvent(LightweightDispatcher.java:4422)
   at java.awt.Container.dispatchEventImpl(Container.java:2273)
   at java.awt.Window.dispatchEventImpl(Window.java:2719)
   at java.awt.Component.dispatchEvent(Component.java:4687)
   at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:729)
   at java.awt.EventQueue.access$200(EventQueue.java:103)
   at java.awt.EventQueue$3.run(EventQueue.java:688)
   at java.awt.EventQueue$3.run(EventQueue.java:686)
   at java.security.AccessController.doPrivileged(AccessController.java:0)
   at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
   at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
   at java.awt.EventQueue$4.run(EventQueue.java:702)
   at java.awt.EventQueue$4.run(EventQueue.java:700)
   at java.security.AccessController.doPrivileged(AccessController.java:0)
   at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
   at java.awt.EventQueue.dispatchEvent(EventQueue.java:699)
   at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:159)
   at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
   at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
   at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
   at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
   at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
   at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)