anchor.diff:  
     @override
     Widget build(BuildContext context) {
  -    if (widget.rootNode == null && widget.nodes.isNotEmpty) {
  +    if (widget.rootNode == null && widget.nodes!.isNotEmpty) {
         // If constructed with Treemap.fromNodes
         return buildSubTreemaps();
       } else {
  
positive.code:   /// ----------------------
    /// ```
    List<PositionedCell> buildTreemaps({
      @required List<TreemapNode> children,
      @required double x,
      @required double y,
      @required double width,
      @required double height,
    }) {
      final isHorizontalRectangle = width > height;
  
  
negative.code:   }
  
    Text buildNameAndSizeText({
      required Color? textColor,
      required bool oneLine,
    }) {
      return Text(
        widget.rootNode!.displayText(oneLine: oneLine),
        style: TextStyle(color: textColor),
        textAlign: TextAlign.center,
        overflow: TextOverflow.ellipsis,
  