Critical Bug: Blazor Server – SignalR NullReferenceException when closing modal and updating QuickGrid

[yvanddivans]

📋 Description

In a Blazor Server app, when a modal component is closed (via @if) and an EventCallback adds an item to a list bound to a QuickGrid, the server crashes with a NullReferenceException in SignalR.

This causes:

• The entire app to freeze
• The SignalR circuit to die silently
• No exception being caught by any ErrorBoundary

🧪 Repro steps

1. A parent component displays a QuickGrid bound to a list: List<InvoiceDetailsModel>
2. A modal component is shown via @if (IsModalVisible)
3. On form submit inside the modal, an EventCallback adds an item to the list and sets IsModalVisible = false
4. This causes Blazor to:
   • Dispose the modal component
   • Re-render the QuickGrid
5. At this point, SignalR crashes with a NullReferenceException

💣 What actually happens

• RemoteJSRuntime.EndInvokeDotNet(...) throws NullReferenceException
• The app freezes completely
• No exception bubbles up
• Reproducible 100% of the time

✅ What has been tried (and failed)

Attempted Fix	Outcome
Using @key to force modal recreation	❌ No effect
Implementing IDisposable and detaching event handlers	✅ Called, no leak — but still crashes
Wrapping EventCallback in InvokeAsync() or Task.Yield()	❌ Still crashes
Resetting bound model before disposal (Detail = new())	❌ Still crashes
Toggling visibility (Visible=true/false) instead of @if	❌ Same behavior
Delaying updates to parent via Task.Delay()	❌ Still crashes
Removing QuickGrid temporarily	✅ Prevents crash → likely trigger is grid rerender

📎 Stack trace

System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.AspNetCore.Components.Server.Circuits.RemoteJSRuntime.EndInvokeDotNet(DotNetInvocationInfo invocationInfo, DotNetInvocationResult& invocationResult)
   at Microsoft.AspNetCore.SignalR.ClientProxyExtensions.SendCoreAsync(...) // decompiled source

🧰 Environment

• .NET 8.0.x
• Blazor Server
• Microsoft.AspNetCore.SignalR.Core (latest)
• Microsoft.AspNetCore.Components.QuickGrid (stable)

🙏 Request

• Can this be addressed in QuickGrid's rendering logic or the framework’s circuit lifecycle?
• At minimum, can the runtime guard against this crash instead of throwing from SendCoreAsync()?
• Should there be documentation or pattern warnings around updating QuickGrid during component disposal?

[ilonatommy]

@dariatiurina, let's check if we can reproduce in net8.

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