Added tests for ComboBox and ComboBoxItem - #656

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, actions/github-script@60a0d83039c74a4aee543508d2ffcb1c3799cdea, actions/setup-dotnet@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Possible null reference argument for parameter 'item' in 'bool HashSet<MudListItemExtended<T?>>.Add(MudListItemExtended<T?> item)'.

Dereference of a possibly null reference.

Possible null reference argument for parameter 'endText' in 'void MudJsonTreeViewNode.GenerateComponent(RenderTreeBuilder builder, string text, string endText, string icon)'.

Dereference of a possibly null reference.

Possible null reference argument for parameter 'jsRuntime' in 'ValueTask JSRuntimeExtensions.InvokeVoidAsync(IJSRuntime jsRuntime, string identifier, params object?[]? args)'.

Dereference of a possibly null reference.

Possible null reference argument for parameter 'collection' in 'HashSet<T?>.HashSet(IEnumerable<T?> collection, IEqualityComparer<T?>? comparer)'.

Dereference of a possibly null reference.

Dereference of a possibly null reference.

Non-nullable field '_timeHourFormat' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the field as nullable.

Dereference of a possibly null reference.

Nullability of reference types in type of parameter 'sender' of 'void MudWatch.Elapse(object sender, ElapsedEventArgs args)' doesn't match the target delegate 'ElapsedEventHandler' (possibly because of nullability attributes).

Dereference of a possibly null reference.

Dereference of a possibly null reference.

Dereference of a possibly null reference.

Dereference of a possibly null reference.

Dereference of a possibly null reference.

Dereference of a possibly null reference.

Dereference of a possibly null reference.

Dereference of a possibly null reference.