anchor.diff:      Key key,
       this.animationController,
       this.enableDrag = true,
  +    this.elevation = 0.0,
       @required this.onClosing,
       @required this.builder
     }) : assert(enableDrag != null),
          assert(onClosing != null),
          assert(builder != null),
  +       assert(elevation != null),
          super(key: key);
   
     /// The animation that controls the bottom sheet's position.
  
positive.code:   ///
    /// Default is true.
    final bool enableDrag;
  
    @override
    _BottomSheetState createState() => _BottomSheetState();
  
negative.code:   Widget build(BuildContext context) {
      final Widget bottomSheet = Material(
        key: _childKey,
        elevation: widget.elevation,
        child: widget.builder(context),
      );
      return !widget.enableDrag ? bottomSheet : GestureDetector(
  