Node.js 20 actions are deprecated. The following actions are running on Node.js 20 and may not work as expected: actions/checkout@v4, actions/upload-artifact@v4. Actions will be forced to run with Node.js 24 by default starting June 2nd, 2026. Node.js 20 will be removed from the runner on September 16th, 2026. Please check if updated versions of these actions are available that support Node.js 24. To opt into Node.js 24 now, set the FORCE_JAVASCRIPT_ACTIONS_TO_NODE24=true environment variable on the runner or in your workflow file. Once Node.js 24 becomes the default, you can temporarily opt out by setting ACTIONS_ALLOW_USE_UNSECURE_NODE_VERSION=true. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Nullability of reference types in type of parameter 'x' of 'int CardSorter.Compare(string x, string y)' doesn't match implicitly implemented member 'int IComparer<string>.Compare(string? x, string? y)' (possibly because of nullability attributes).

Cannot convert null literal to non-nullable reference type.

Cannot convert null literal to non-nullable reference type.

Cannot convert null literal to non-nullable reference type.

Nullability of type of parameter 'message' doesn't match overridden member (possibly because of nullability attributes).

Nullability of type of parameter 'message' doesn't match overridden member (possibly because of nullability attributes).

Dereference of a possibly null reference.

Possible null reference assignment.

Possible null reference assignment.