anchor.diff:      this.maxLines,
       Curve curve = Curves.linear,
       @required Duration duration,
  -    Duration reverseDuration,
     }) : assert(style != null),
          assert(child != null),
          assert(softWrap != null),
          assert(overflow != null),
          assert(maxLines == null || maxLines > 0),
  -       super(key: key, curve: curve, duration: duration, reverseDuration: reverseDuration);
  +       super(key: key, curve: curve, duration: duration);
   
     /// The widget below this widget in the tree.
     ///
  
positive.code:     Key key,
      this.curve = Curves.linear,
      @required this.duration,
      this.reverseDuration,
    }) : assert(curve != null),
         assert(duration != null),
         super(key: key);
  
negative.code:     this.height,
      Curve curve = Curves.linear,
      @required Duration duration,
    }) : assert(start == null || end == null || width == null),
         assert(top == null || bottom == null || height == null),
         super(key: key, curve: curve, duration: duration);
  
    /// The widget below this widget in the tree.
    ///
  