anchor.diff:  
   class AspectRatio extends OneChildRenderObjectWrapper {
     AspectRatio({ Key key, this.aspectRatio, Widget child })
  -    : super(key: key, child: child);
  +    : super(key: key, child: child) {
  +    assert(aspectRatio != null);
  +  }
   
     final double aspectRatio;
   
  
positive.code: 
  class Padding extends OneChildRenderObjectWrapper {
    Padding({ Key key, this.padding, Widget child })
      : super(key: key, child: child);
  
    final EdgeDims padding;
  
  
negative.code:     this.scrollDirection: ScrollDirection.vertical,
      this.scrollOffset: Offset.zero,
      Widget child
    }) : super(key: key, child: child) {
      assert(scrollDirection != null);
      assert(scrollOffset != null);
    }
  
    final ScrollDirection scrollDirection;
    final Offset scrollOffset;
  