microsoft/aspire · error · ArgumentNullException

ArgumentNullException for parameter 'resource' (resource is…

Error message

ArgumentNullException for parameter 'resource' (resource is null).

What it means

ContainerBuildOptionsCallbackContext's constructor validates that the IResource it is created for is not null. The context carries the resource whose container build options are being configured; without a resource the context is meaningless, so the constructor throws ArgumentNullException.

Solutions

Pass a valid IResource instance (e.g. the resource the annotation is attached to).
In tests, initialize the resource before creating the context (e.g. new MyResource("name")).
Check earlier code for a null resource flowing through (nullable annotations should flag it).

Example fix

// before
var ctx = new ContainerBuildOptionsCallbackContext(resource!, services, logger, ct, execCtx); // resource null at runtime

// after
var ctx = new ContainerBuildOptionsCallbackContext(new CustomResource("mycontainer"), services, logger, ct, execCtx);

Defensive patterns

Strategy: validation

Validate before calling

if (resource is null) throw new InvalidOperationException("Cannot create ContainerBuildOptionsCallbackContext without a resource.");

Type guard

bool CanBuildContext(IResource? r) => r is not null;

Try / catch

try { var ctx = new ContainerBuildOptionsCallbackContext(resource, services, logger, ct, execCtx); }
catch (ArgumentNullException ex) when (ex.ParamName == "resource") { logger.LogError(ex, "Resource missing when building callback context"); }

Prevention

Pass the resource from the annotation/execution context rather than a separately tracked variable.
In tests, construct a concrete resource instance before building the context.
Enable nullable reference types so a null resource is flagged at compile time.

When it happens

Trigger: Constructing ContainerBuildOptionsCallbackContext directly (tests, custom pipeline code) with a null resource argument.

Common situations: Unit tests building a fake context where the resource fixture wasn't initialized; custom execution-context code that lost track of the current resource.

Related errors

AI-assisted analysis of microsoft/aspire@25830f84bd (2026-09-16). Data as JSON: /api/errors/9c7145bb8621f816. Report an issue: GitHub.

Appendix: source

Thrown at src/Aspire.Hosting/ApplicationModel/ContainerBuildOptionsCallbackAnnotation.cs:58

[AspireExport(ExposeProperties = true)]
public sealed class ContainerBuildOptionsCallbackContext
{
    /// <summary>
    /// Initializes a new instance of <see cref="ContainerBuildOptionsCallbackContext"/>.
    /// </summary>
    /// <param name="resource">The resource being built.</param>
    /// <param name="services">The service provider.</param>
    /// <param name="logger">The logger instance.</param>
    /// <param name="cancellationToken">The cancellation token.</param>
    /// <param name="executionContext">The distributed application execution context.</param>
    public ContainerBuildOptionsCallbackContext(
        IResource resource,
        IServiceProvider services,
        ILogger logger,
        CancellationToken cancellationToken,
        DistributedApplicationExecutionContext executionContext)
    {
        Resource = resource ?? throw new ArgumentNullException(nameof(resource));
        Services = services ?? throw new ArgumentNullException(nameof(services));
        Logger = logger ?? throw new ArgumentNullException(nameof(logger));
        CancellationToken = cancellationToken;
        ExecutionContext = executionContext ?? throw new ArgumentNullException(nameof(executionContext));
    }

    /// <summary>
    /// Gets the resource being built.
    /// </summary>
    public IResource Resource { get; }

    /// <summary>
    /// Gets the service provider.
    /// </summary>
    public IServiceProvider Services { get; }

    /// <summary>
    /// Gets the logger instance.

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