AvaloniaUI/Avalonia · info · ArgumentNullException

stack

Error message

stack

What it means

Constructor null guard in the internal StackDebugView<T> debugger proxy: `stack ?? throw new ArgumentNullException(nameof(stack))`. Like ICollectionDebugView, this is a DebuggerTypeProxy used by the IDE to render a PooledStack; it is not part of the user-facing runtime API. It only fires when the proxy is constructed for a null stack.

Source

Thrown at src/Avalonia.Base/Collections/Pooled/StackDebugView.cs:16

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

using System;
using System.Diagnostics;

namespace Avalonia.Collections.Pooled
{
    internal sealed class StackDebugView<T>
    {
        private readonly PooledStack<T> _stack;

        public StackDebugView(PooledStack<T> stack)
        {
            _stack = stack ?? throw new ArgumentNullException(nameof(stack));
        }

        [DebuggerBrowsable(DebuggerBrowsableState.RootHidden)]
        public T[] Items
        {
            get
            {
                return _stack.ToArray();
            }
        }
    }
}

View on GitHub (pinned to 11c5427268)

Solutions

1. Initialize the stack field so it is non-null before inspection.
2. Ignore it — this originates from the debugger proxy, not your executed code path.
3. In a test that builds the proxy directly, pass a non-null PooledStack.

// Debugger-only proxy; ensure PooledStack fields are non-null before inspection.
// No runtime validation path in product code.

When it happens

Trigger: The debugger instantiates StackDebugView for a PooledStack field/variable that is null while browsing Locals/Watch, or direct construction `new StackDebugView<T>(null)` in a test.

Common situations: Inspecting an uninitialized/null PooledStack field in the debugger; a debug session showing a stack before assignment. The throw is debugger-scoped and does not occur in a normal run.

Related errors

• collection
• array
• Destination span is shorter than the list to be copied.
• Stack was empty.
• Collection was modified during enumeration.

AI-assisted analysis of AvaloniaUI/Avalonia@11c5427268 (2026-08-13). Data as JSON: /api/errors/02e8bd86e8348f25. Report an issue: GitHub.