anchor.diff:      _curve = null;
       _controller?.stop();
       _controller = null;
  -    _key.stopMimic();
  -    _key = null;
  +    _handle.stopMimic();
  +    _handle = null;
       _overlayEntry.remove();
       _overlayEntry = null;
     }
   
     Widget _build(BuildContext context) {
  -    assert(_key != null);
  +    assert(_handle != null);
       assert(_overlayEntry != null);
       Rect globalBounds = _initialGlobalBounds;
       Point globalPosition = globalBounds.topLeft;
  
positive.code: 
  /// An overlay entry that is mimicking another widget.
  class MimicOverlayEntry {
    MimicOverlayEntry._(this._key) {
      _overlayEntry = new OverlayEntry(builder: _build);
      _initialGlobalBounds = _key.globalBounds;
    }
  
    Rect _initialGlobalBounds;
  
    MimicableHandle _key;
    OverlayEntry _overlayEntry;
  
    // Animation state
  
negative.code:       top: localPosition.y,
        width: globalBounds.width,
        height: globalBounds.height,
        child: new Mimic(original: _handle)
      );
    }
  }
  