microsoft/aspire · error · ArgumentNullException

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

Error message

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

What it means

Primary constructor null guard in CommandLineArgsCallbackContext: the 'args' list argument is null. The context wraps the caller's argument list to mutate it in place, so a null list has nothing to wrap and every subsequent editor operation would fail.

Solutions

Pass a concrete list, e.g. new List<object>() or resource annotations' args list
Initialize the args collection before constructing the context

Example fix

// before
var ctx = new CommandLineArgsCallbackContext(null, resource);
// after
var ctx = new CommandLineArgsCallbackContext(new List<object>(), resource);

Defensive patterns

Strategy: validation

Validate before calling

var argsList = args ?? new List<object>();

Prevention

Initialize args lists with new List<object>() before constructing contexts
Never pass possibly-null collections into context constructors

When it happens

Trigger: new CommandLineArgsCallbackContext(null, resource) or the 2-arg overload with a null IList<object>.

Common situations: Manually constructing the context in tests or custom pipelines with an uninitialized args list; a method returning null args passed straight through.

Related errors

AI-assisted analysis of microsoft/aspire@25830f84bd (2026-09-16). Data as JSON: /api/errors/a72006455bee795f. Report an issue: GitHub.

Appendix: source

Thrown at src/Aspire.Hosting/ApplicationModel/CommandLineArgsCallbackAnnotation.cs:112

/// <param name="cancellationToken"> The cancellation token associated with this execution.</param>
[AspireExport]
public sealed class CommandLineArgsCallbackContext(IList<object> args, CancellationToken cancellationToken = default)
{
    private readonly IResource? _resource;

    /// <summary>
    /// Represents a callback context for the list of command-line arguments associated with an executable resource.
    /// </summary>
    /// <param name="args"> The list of command-line arguments.</param>
    /// <param name="resource"> The resource associated with this callback context.</param>
    /// <param name="cancellationToken"> The cancellation token associated with this execution.</param>
    public CommandLineArgsCallbackContext(IList<object> args, IResource resource, CancellationToken cancellationToken = default)
        : this(args, cancellationToken) => _resource = resource ?? throw new ArgumentNullException(nameof(resource));

    /// <summary>
    /// Gets the list of command-line arguments.
    /// </summary>
    public IList<object> Args { get; } = args ?? throw new ArgumentNullException(nameof(args));

    /// <summary>
    /// Gets the cancellation token associated with the callback context.
    /// </summary>
    public CancellationToken CancellationToken { get; } = cancellationToken;

    /// <summary>
    /// Gets or sets the execution context for the distributed application.
    /// </summary>
    public DistributedApplicationExecutionContext ExecutionContext { get; init; } = new(DistributedApplicationOperation.Run);

    /// <summary>
    /// Gets or sets the logger for the distributed application.
    /// </summary>
    public ILogger Logger { get; init; } = NullLogger.Instance;

    /// <summary>
    /// Gets the editor used to manipulate command-line arguments in polyglot callbacks.

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