Null check operator used on a null value about flutter_parallax

[elmobark]

@letsar @YAPEIZG i think this project is dead the creator is not answering , so the best thing to do is to fork the project and fix the problem b your self :(

[Gastrolize]

change in file rendering/parallax.dart the method getChildScrollRatio into:

 @override
  double getChildScrollRatio(
      Offset offsetUnit, double childExtent, RenderBox renderBox) {
    final RenderAbstractViewport viewport =
        RenderAbstractViewport.of(renderBox);
    assert(viewport != null);


    assert(renderBox != null);
    final ScrollPosition position = controller.position;
    assert(position != null);
    final bool isHorizontalAxis = (position.axis == Axis.horizontal);


    final Offset localPositionOffset = isHorizontalAxis
        ? new Offset(mainAxisExtent, 0.0)
        : new Offset(0.0, mainAxisExtent);//offsetUnit * mainAxisExtent;

    assert(localPositionOffset != null);
    Offset positionInViewport;
    try{
      positionInViewport = renderBox.localToGlobal(localPositionOffset, ancestor: viewport);
    } catch(e,s){

    }
    if(positionInViewport == null){
      return 0;
    }

    // One dimension should be 0.0, so this should be ok.
    final double distanceFromLeading =
        math.max(positionInViewport.dx, positionInViewport.dy);
    assert(distanceFromLeading != null);
    double scrollRatio = distanceFromLeading /
        (controller.position.viewportDimension + mainAxisExtent);
    return scrollRatio;
  }

This Error appears when the Widget is building and the method trys to access the viewport.
This should fix and return 0 while building the widget.