anchor.diff:    _CupertinoAlertRenderWidget get widget => super.widget as _CupertinoAlertRenderWidget;
   
     @override
  -  _RenderCupertinoAlert? get renderObject => super.renderObject as _RenderCupertinoAlert?;
  +  _RenderCupertinoAlert get renderObject => super.renderObject as _RenderCupertinoAlert;
   
     @override
     void visitChildren(ElementVisitor visitor) {
  
positive.code:     assert(slot != null);
      switch (slot) {
        case _AlertSections.contentSection:
          renderObject!.contentSection = child as RenderBox;
          break;
        case _AlertSections.actionsSection:
          renderObject!.actionsSection = child as RenderBox;
          break;
      }
    }
  
negative.code: 
    @override
    void removeRenderObjectChild(RenderObject child, _AlertSections slot) {
      assert(child == renderObject.contentSection || child == renderObject.actionsSection);
      if (renderObject.contentSection == child) {
        renderObject.contentSection = null;
      } else if (renderObject.actionsSection == child) {
        renderObject.actionsSection = null;
      }
    }
  
  