microsoft/aspire · error · ArgumentException

Error message cannot be null or empty.

Error message

Error message cannot be null or empty.

What it means

InteractionBuilder.AddValidationError validates that errorMessage is non-null and non-empty before attaching it to the input's ValidationErrors. An empty message would produce useless UI feedback, so ArgumentException is thrown eagerly.

Solutions

1. Pass a descriptive, non-empty message such as "Value is required".
2. Guard caller-supplied messages before calling AddValidationError.
3. If the message may be absent, skip the call instead of adding an empty error.

Example fix

// before
prompt.AddValidationError(input, string.Empty);
// after
prompt.AddValidationError(input, "A value for this input is required.");

if (!string.IsNullOrWhiteSpace(errorMessage))
{
    prompt.AddValidationError(input, errorMessage);
}

static bool IsValidMessage(string? m) => !string.IsNullOrWhiteSpace(m);

try
{
    prompt.AddValidationError(input, errorMessage);
}
catch (ArgumentException ex) when (ex.ParamName == nameof(errorMessage))
{
    logger.LogError(ex, "Skipped empty validation message for {Input}", input.Name);
}

When it happens

Trigger: Calling AddValidationError(input, null) or AddValidationError(input, "") or passing a whitespace/empty result of a variable or function producing the message.

Common situations: Building the message via string interpolation that yields empty (e.g. from a missing resource string); passing through a caller-supplied message that was not checked.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

• Must not be null or empty
• Must not be null or empty
• Must not be null or whitespace
• Must not be null or whitespace
• Submitted files for input

AI-assisted analysis of microsoft/aspire@25830f84bd (2026-09-16). Data as JSON: /api/errors/f2116639c4514f3d. Report an issue: GitHub.

Appendix: source

Thrown at src/Aspire.Hosting/IInteractionService.cs:857

    public required CancellationToken CancellationToken { get; init; }

    /// <summary>
    /// Gets the service provider for resolving services during validation.
    /// </summary>
    public required IServiceProvider Services { get; init; }

    /// <summary>
    /// Adds a validation error for the specified input.
    /// </summary>
    /// <param name="input">The input to add a validation error for.</param>
    /// <param name="errorMessage">The error message to add.</param>
    public void AddValidationError(InteractionInput input, string errorMessage)
    {
        ArgumentNullException.ThrowIfNull(input, nameof(input));

        if (string.IsNullOrEmpty(errorMessage))
        {
            throw new ArgumentException("Error message cannot be null or empty.", nameof(errorMessage));
        }

        input.ValidationErrors.Add(errorMessage);
        HasErrors = true;
    }

    /// <summary>
    /// Adds a validation error for the input with the specified name.
    /// </summary>
    /// <param name="inputName">The name of the input to add a validation error for.</param>
    /// <param name="errorMessage">The error message to add.</param>
    [AspireExport("InputsDialogValidationContext.addValidationError", MethodName = "addValidationError")]
    public void AddValidationError(string inputName, string errorMessage)
    {
        AddValidationError(Inputs[inputName], errorMessage);
    }
}

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