microsoft/aspire · error · ArgumentNullException

innerResource

Error message

innerResource

What it means

The AzureServiceBusEmulatorResource constructor stores the real (provisioned) AzureServiceBusResource it wraps and throws ArgumentNullException when the innerResource argument is null. The emulator resource delegates Annotations to the inner resource, so null is invalid by construction.

Solutions

1. Always construct via builder.RunAsEmulator() rather than new AzureServiceBusEmulatorResource(...) directly.
2. If constructing manually, pass the non-null AzureServiceBusResource from the resource builder (builder.Resource).
3. Guard with ArgumentNullException.ThrowIfNull in your own factory before calling the constructor.

Example fix

// before
var emulator = new AzureServiceBusEmulatorResource(null!);
// after
var emulator = new AzureServiceBusEmulatorResource(builder.Resource);

if (innerResource is null)
{
    throw new ArgumentNullException(nameof(innerResource), "Provide the AzureServiceBusResource to wrap.");
}
var emulator = new AzureServiceBusEmulatorResource(innerResource);

static AzureServiceBusResource? TryGetInnerResource(IResource? r) => r as AzureServiceBusResource;

When it happens

Trigger: Calling new AzureServiceBusEmulatorResource(null) — directly or via RunAsEmulator internals — instead of passing the AzureServiceBusResource returned by AddAzureServiceBus.

Common situations: Hand-constructing the emulator resource in tests or custom code and passing a null builder resource; reflection-based instantiation with missing arguments; refactor dropped the argument.

Related errors

• parent
• The Azure Service Bus resource is already configured to run…
• The configuration file mount could not be parsed.
• Dashboard endpoint is only available when running as an…
• Emulator currently does not support data lake.

AI-assisted analysis of microsoft/aspire@25830f84bd (2026-09-16). Data as JSON: /api/errors/6fbfa5199c95cf8d. Report an issue: GitHub.

Appendix: source

Thrown at src/Aspire.Hosting.Azure.ServiceBus/AzureServiceBusEmulatorResource.cs:19

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using Aspire.Hosting.ApplicationModel;

namespace Aspire.Hosting.Azure;

/// <summary>
/// Wraps an <see cref="AzureServiceBusResource" /> in a type that exposes container extension methods.
/// </summary>
/// <param name="innerResource">The inner resource used to store annotations.</param>
public class AzureServiceBusEmulatorResource(AzureServiceBusResource innerResource) : ContainerResource(innerResource.Name), IResource
{
    // The path to the emulator configuration files in the container.
    internal const string EmulatorConfigFilesPath = "/ServiceBus_Emulator/ConfigFiles";
    // The path to the emulator configuration file in the container.
    internal const string EmulatorConfigJsonFile = "Config.json";

    private readonly AzureServiceBusResource _innerResource = innerResource ?? throw new ArgumentNullException(nameof(innerResource));

    /// <inheritdoc />
    public override ResourceAnnotationCollection Annotations => _innerResource.Annotations;
}

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