anchor.diff:  class SlideTransition extends AnimatedWidget {
     /// Creates a fractional translation transition.
     ///
  -  /// The [position] argument is required.
  +  /// The [position] argument must not be null.
     SlideTransition({
       Key key,
  -    Animation<FractionalOffset> position,
  +    @required Animation<FractionalOffset> position,
       this.transformHitTests: true,
       this.child,
     }) : super(key: key, listenable: position);
  
positive.code: class RotationTransition extends AnimatedWidget {
    /// Creates a rotation transition.
    ///
    /// The [turns] argument is required.
    RotationTransition({
      Key key,
      Animation<double> turns,
      this.child,
    }) : super(key: key, listenable: turns);
  
  
negative.code:   ///
    /// Each frame, the [Positioned] widget will be configured to represent the
    /// current value of the [rect] argument assuming that the stack has the given
    /// [size]. Both [rect] and [size] must not be null.
    RelativePositionedTransition({
      Key key,
      @required Animation<Rect> rect,
  