java.lang.AssertionError
   at org.netbeans.modules.css.model.api.ModelUtils.findMatchingRule(ModelUtils.java:135)
   at org.netbeans.modules.css.visual.RuleEditorPanel$6.run(RuleEditorPanel.java:519)
   at org.netbeans.modules.css.model.api.Model$1.run(Model.java:277)
   at org.openide.util.Mutex.readAccess(Mutex.java:367)
   at org.netbeans.modules.css.model.api.Model.runReadTask(Model.java:274)
   at org.netbeans.modules.css.visual.RuleEditorPanel.setModel(RuleEditorPanel.java:515)
   at org.netbeans.modules.css.visual.api.RuleEditorController$1.run(RuleEditorController.java:159)
   at org.openide.util.Mutex.doEvent(Mutex.java:1343)
   at org.openide.util.Mutex.readAccess(Mutex.java:350)
   at org.netbeans.modules.css.visual.api.RuleEditorController.setModel(RuleEditorController.java:156)
   at org.netbeans.modules.css.visual.CssCaretAwareSourceTask.runInEDT(CssCaretAwareSourceTask.java:196)
   at org.netbeans.modules.css.visual.CssCaretAwareSourceTask.access$000(CssCaretAwareSourceTask.java:74)
   at org.netbeans.modules.css.visual.CssCaretAwareSourceTask$1.run(CssCaretAwareSourceTask.java:126)
   at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
   at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:721)
   at java.awt.EventQueue.access$200(EventQueue.java:103)
   at java.awt.EventQueue$3.run(EventQueue.java:682)
   at java.awt.EventQueue$3.run(EventQueue.java:680)
   at java.security.AccessController.doPrivileged(AccessController.java:0)
   at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
   at java.awt.EventQueue.dispatchEvent(EventQueue.java:691)
   at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:159)
   at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:244)
   at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:163)
   at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
   at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:147)
   at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:139)
   at java.awt.EventDispatchThread.run(EventDispatchThread.java:97)