Null Safety issue on the given example!

[kishan-dhankecha]

Page URL

https://docs.flutter.dev/cookbook/effects/shimmer-loading/

Page source

https://github.com/flutter/website/tree/main/src/content/cookbook/effects/shimmer-loading.md

Describe the problem

There is an issue with the code provided in the example below. When I copied the whole code from the interactive editor in the website and pasted it into my project to use the ShimmerLoading widget, I found that I get the classic Null check operator used on a null value error. See the issue in the below snippet.

// Collect ancestor shimmer information.
final shimmer = Shimmer.of(context)!; /// Error comes from this line
if (!shimmer.isSized) {
  // The ancestor Shimmer widget isn't laid
  // out yet. Return an empty box.
  return const SizedBox();
}

Expected fix

It should be changed to this,

// Collect ancestor shimmer info.
final shimmer = Shimmer.of(context);
if (shimmer == null || !shimmer.isSized) {
  // The ancestor Shimmer widget has not laid
  // itself out yet. Return an empty box.
  return const SizedBox();
}

Additional context

No response

I would like to fix this problem.

• I will try and fix this problem on docs.flutter.dev.

[sfshaza2]

@kishan-dhankecha, what version of Flutter/Dart are you using? shimmer is defined as never being null. So, testing for null isn't necessary. The only thing that makes sense is that you are using an older version of Dart.

[kishan-dhankecha]

Note that this issue of null check only happens when a user forgets to wrap the widget with Shimmer. In that case, context will not find the Shimmer on the upper side of the tree.

[sfshaza2]

@domesticmouse, can you weigh in on this?

[domesticmouse]

Given this is an exception that is only thrown when the developer goofs, I don't see the need to make the suggested change. I'd prefer the code to break, given it is already broken.

[kishan-dhankecha]

Yes, @domesticmouse you are right here. It would help more if the developer discovered this if they made this mistake.

I am closing this. Thanks.