Error: A value of type 'bool?' can't be assigned to a variable of type 'bool' because 'bool?' is nullable and 'bool' isn't

Question

I get this error when i try to build my app.

 Error: A value of type 'bool?' can't be assigned to a variable of type 'bool' because 'bool?' is nullable and 'bool' isn't.
            (childView.primary ? PrimaryScrollController.of(context) : null);
                       ^

Here is my complete code:

  // build the customScrollView
  Widget? _buildBodyBySlivers(
      Widget? childView, List<Widget>? slivers, RefreshConfiguration? conf) {
    Widget? body;
    if (childView is! Scrollable) {
      bool? primary = widget.primary;
      Key? key;
      double? cacheExtent = widget.cacheExtent;

      Axis? scrollDirection = widget.scrollDirection;
      int? semanticChildCount = widget.semanticChildCount;
      bool? reverse = widget.reverse;
      ScrollController? scrollController = widget.scrollController;
      DragStartBehavior? dragStartBehavior = widget.dragStartBehavior;
      ScrollPhysics? physics = widget.physics;
      Key? center;
      double? anchor;
      ScrollViewKeyboardDismissBehavior? keyboardDismissBehavior;
      String? restorationId;
      Clip? clipBehavior;

      if (childView is ScrollView) {
        primary = primary ?? childView.primary;
        cacheExtent = cacheExtent ?? childView.cacheExtent;
        key = key ?? childView.key;
        semanticChildCount = semanticChildCount ?? childView.semanticChildCount;
        reverse = reverse ?? childView.reverse;
        dragStartBehavior = dragStartBehavior ?? childView.dragStartBehavior;
        scrollDirection = scrollDirection ?? childView.scrollDirection;
        physics = physics ?? childView.physics;
        center = center ?? childView.center;
        anchor = anchor ?? childView.anchor;
        keyboardDismissBehavior =
            keyboardDismissBehavior ?? childView.keyboardDismissBehavior;
        restorationId = restorationId ?? childView.restorationId;
        clipBehavior = clipBehavior ?? childView.clipBehavior;
        scrollController = scrollController ?? childView.controller;

        // ignore: DEPRECATED_MEMBER_USE_FROM_SAME_PACKAGE
        widget.controller.scrollController = scrollController ??
            childView.controller ??
            (childView.primary ? PrimaryScrollController.of(context) : null);
      } else {
        // ignore: DEPRECATED_MEMBER_USE_FROM_SAME_PACKAGE
        widget.controller.scrollController =
            PrimaryScrollController.of(context);
      }
      body = CustomScrollView(
        // ignore: DEPRECATED_MEMBER_USE_FROM_SAME_PACKAGE
        controller: scrollController,
        cacheExtent: cacheExtent,
        key: key,
        scrollDirection: scrollDirection ?? Axis.vertical,
        semanticChildCount: semanticChildCount,
        primary: primary,
        clipBehavior: clipBehavior ?? Clip.hardEdge,
        keyboardDismissBehavior:
            keyboardDismissBehavior ?? ScrollViewKeyboardDismissBehavior.manual,
        anchor: anchor ?? 0.0,
        restorationId: restorationId,
        center: center,
        physics:
            _getScrollPhysics(conf, physics ?? AlwaysScrollableScrollPhysics()),
        slivers: slivers!,
        dragStartBehavior: dragStartBehavior ?? DragStartBehavior.start,
        reverse: reverse ?? false,
      );
    } else if (childView is Scrollable) {
      body = Scrollable(
        physics: _getScrollPhysics(
            conf, childView.physics ?? AlwaysScrollableScrollPhysics()),
        controller: childView.controller,
        axisDirection: childView.axisDirection,
        semanticChildCount: childView.semanticChildCount,
        dragStartBehavior: childView.dragStartBehavior,
        viewportBuilder: (context, offset) {
          Viewport viewport = childView.viewportBuilder(context, offset) as Viewport;
          if (widget.enablePullDown) {
            viewport.children.insert(
                0,
                widget.header ??
                    (conf?.headerBuilder != null
                        ? conf?.headerBuilder!()
                        : null) ??
                    defaultHeader);
          }

When I try to build apk with flutter it says this error on the title. I didn't understand what the problem is because I am new on development. Thanks in advance.

Also I've checked this subject but still didn't understand the solution : A value of type 'bool?' can't be assigned to a variable of type 'bool' because 'bool?' is nullable and 'bool' isn't

Answer 1

I would suggest to get familiar what is null-safety. Check the anwer here: Dart, Identifier with exclamation mark in the back.

The childView's primary parameter is of type bool, you can't assign null to it cause its accepting only bool values and it's non-nullable. Only types with question mark are nullable and you can assign null to them.