anchor.diff:  
     @override
     void didChangeDependencies() {
  -    _mediaQueryData = MediaQuery.maybeOf(context);
       _updatePosition();
       super.didChangeDependencies();
     }
  
positive.code:   late ScrollBehavior _configuration;
    ScrollPhysics? _physics;
    ScrollController? _fallbackScrollController;
    MediaQueryData? _mediaQueryData;
  
    ScrollController get _effectiveScrollController => widget.controller ?? _fallbackScrollController!;
  
  
negative.code:                   ..minFlingVelocity = _physics?.minFlingVelocity
                    ..maxFlingVelocity = _physics?.maxFlingVelocity
                    ..velocityTrackerBuilder = _configuration.velocityTrackerBuilder(context)
                    ..dragStartBehavior = widget.dragStartBehavior;
                },
              ),
            };
  