anchor.diff:         assert(shadowColor != null),
          assert(animateColor != null),
          assert(animateShadowColor != null),
  -       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:     @required this.opacity,
      Curve curve = Curves.linear,
      @required Duration duration,
      Duration reverseDuration,
    }) : assert(opacity != null && opacity >= 0.0 && opacity <= 1.0),
         super(key: key, curve: curve, duration: duration, reverseDuration: reverseDuration);
  
    /// The widget below this widget in the tree.
    ///
  
negative.code:     this.child,
      Curve curve = Curves.linear,
      @required Duration duration,
    }) : assert(margin == null || margin.isNonNegative),
         assert(padding == null || padding.isNonNegative),
         assert(decoration == null || decoration.debugAssertIsValid()),
  