[Blazor] Static SSR - [SupplyParameterFromForm] parameter null on empty form data (eg. unchecked InputCheckbox)

[hakenr]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

With Static SSR and [SupplyParameterFromForm], the value of the parameter from constructor is lost and the parameter is assigned null when on "empty" form data (eg. unchecked InputCheckbox).

<EditForm Model="_model" FormName="my-form">
	<DataAnnotationsValidator />
	<ValidationSummary />
	<InputCheckbox @bind-Value="_model.RememberMe" />
	<button type="submit">Submit</button>
</EditForm>

@_model?.RememberMe

@code {
	[SupplyParameterFromForm] private InputModel _model { get; set; } = new();

	private record InputModel
	{
		public bool RememberMe { get; set; }
	}
}

When you click Submit, you get InvalidOperationException: EditForm requires either a Model parameter, or an EditContext parameter, please provide one of these.

Expected Behavior

The example above should end up with a _model parameter assigned to a InputModel instance with the RememberMe property to false.

Steps To Reproduce

See the sample above.
The POSTed form data is

_handler=my-form&__RequestVerificationToken=...

Exceptions (if any)

No response

.NET Version

9.0.2

Anything else?

If I replace the constructor initialization with OnInitialized initialization, the property value is incorrect (true with the repro below):

<EditForm Model="_model" FormName="my-form">
	<DataAnnotationsValidator />
	<ValidationSummary />
	<InputCheckbox @bind-Value="_model.RememberMe" />
	<button type="submit">Submit</button>
</EditForm>

@_model?.RememberMe

@code {
	[SupplyParameterFromForm] private InputModel _model { get; set; }

	protected override void OnInitialized() => _model ??= new InputModel();

	private record InputModel
	{
		public bool RememberMe { get; set; } = true;
	}
}