What causes "Object must be initialized before it can be used" in microsoft/aspire?

Pass a non-null configure action; if customization is conditional, only add the annotation when the action exists

microsoft/aspire · error · ArgumentNullException

Object must be initialized before it can be used

Error message

Object must be initialized before it can be used

What it means

Thrown by the KubernetesServiceCustomizationAnnotation primary constructor when the configure delegate is null. The annotation stores the Action<KubernetesResource> via a null-coalescing ArgumentNullException check because a customization with no action is meaningless.

Solutions

Pass a non-null configure action; if customization is conditional, only add the annotation when the action exists
Replace the null delegate with a no-op: _ => { }
Check upstream API that produced the delegate for accidental null returns

Example fix

// before
Action<KubernetesResource>? configure = condition ? Configure : null;
resource.Annotations.Add(new KubernetesServiceCustomizationAnnotation(configure!));
// after
if (condition)
{
    resource.Annotations.Add(new KubernetesServiceCustomizationAnnotation(Configure));
}

Defensive patterns

Strategy: validation

Validate before calling

if (configure is null) throw new InvalidOperationException("Kubernetes customization action must not be null");

Try / catch

try { resource.Annotations.Add(new KubernetesServiceCustomizationAnnotation(configure)); }
catch (ArgumentNullException) { /* supply a real delegate or skip the annotation */ }

Prevention

Only add the annotation when a real configure action exists
Use _ => { } for intentional no-op customization
Avoid nullable delegates flowing into annotation constructors

When it happens

Trigger: Calling the annotation constructor (directly or through a WithCustomization-style API) passing a null Action<KubernetesResource>, e.g. passing a local method group that is null or a lambda variable that was never assigned.

Common situations: Conditional customization code like Action<KubernetesResource> cfg = condition ? Configure : null followed by adding the annotation unconditionally; reflection or DI scenarios supplying a null delegate.

Related errors

AI-assisted analysis of microsoft/aspire@25830f84bd (2026-09-16). Data as JSON: /api/errors/ca33e2df63c9413f. Report an issue: GitHub.

Appendix: source

Thrown at src/Aspire.Hosting.Kubernetes/KubernetesServiceCustomizationAnnotation.cs:20

// The .NET Foundation licenses this file to you under the MIT license.

using Aspire.Hosting.ApplicationModel;

namespace Aspire.Hosting.Kubernetes;

/// <summary>
/// Represents an annotation for customizing a Kubernetes service.
/// </summary>
/// <remarks>
/// Initializes a new instance of the <see cref="KubernetesServiceCustomizationAnnotation"/> class.
/// </remarks>
/// <param name="configure">The configuration action for customizing the Kubernetes service.</param>
public sealed class KubernetesServiceCustomizationAnnotation(Action<KubernetesResource> configure) : IResourceAnnotation
{
    /// <summary>
    /// Gets the configuration action for customizing the Kubernetes service.
    /// </summary>
    public Action<KubernetesResource> Configure { get; } = configure ?? throw new ArgumentNullException(nameof(configure));
}

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