[Blazor] Supplying a `null` parameter value to an interactive root component causes a `NullReferenceException` on enhanced navigation

[MackinnonBuck]

Summary

If a null value is supplied as a parameter to a render mode boundary component during static SSR, and the SSR'd component is matched up with an existing interactive root component, a NullReferenceException gets thrown by the framework.

Steps to reproduce

1. Create a Blazor Web App with Server interactivity
2. Define a component (MyComponent.razor):

   @inject NavigationManager NavigationManager
   
   <button @onclick="@(() => NavigationManager.Refresh())">Refresh</button>
   
   @code {
       [Parameter]
       public string? Value { get; set; }
   }

3. Render the component from Home.razor and supply the value null for the Value parameter:

   <MyComponent Value="@null" @rendermode="InteractiveServer" />

4. Run the app
5. Click the button labeled "Refresh"
6. Observe that an exception gets thrown and the circuit gets terminated

Relevant output

Stack trace:

Microsoft.AspNetCore.Components.Server.dll!Microsoft.AspNetCore.Components.WebRootComponentParameters.DefinitelyEquals(Microsoft.AspNetCore.Components.WebRootComponentParameters other) Line 43
	at Microsoft.AspNetCore.Components\WebRootComponentParameters.cs(43)
Microsoft.AspNetCore.Components.Server.dll!Microsoft.AspNetCore.Components.Server.Circuits.RemoteRenderer.WebRootComponentManager.WebRootComponent.UpdateAsync(Microsoft.AspNetCore.Components.Server.Circuits.RemoteRenderer renderer, System.Type newComponentType, Microsoft.AspNetCore.Components.ComponentMarkerKey? newKey, Microsoft.AspNetCore.Components.WebRootComponentParameters newParameters) Line 245
	at Microsoft.AspNetCore.Components.Server.Circuits\RemoteRenderer.cs(245)
.
.
.

Proposed fix

Update WebRootComponentParameters to account for the possibility that the parameter values are null rather than being valid JsonElements.

[javiercn]

@MackinnonBuck good catch.

Do you think this has been the case since the beginning or is this a new .NET 8.0 behavior.

[MackinnonBuck]

@javiercn WebRootComponentParameters was a type we introduced in .NET 8, so it only affects .NET 8 (specifically Blazor Web apps; pure Server or WebAssembly apps shouldn't be affected)

[javiercn]

@MackinnonBuck @mkArtakMSFT parking this in 8.0.x as I think it is patchable, feel free to move it otherwise