anchor.diff:    }
   
     void _updateEnablement(ws.Resource resource) {
  -    enabled = _appliesTo(resource);
  +    enabled = resource != null && _appliesTo(resource);
     }
   
     void _toggleProgressVisible(bool visible) {
  
positive.code:   }
  
    void _updateEnablement(ws.Resource resource) {
      enabled = getAppContainerFor(resource) != null;
    }
  }
  
  
negative.code:   }
  
    void _updateEnablement(ws.Resource resource) {
      enabled = (resource != null && _appliesTo(resource));
    }
  }
  
  