microsoft/aspire · error · ArgumentException

Must not be null or whitespace

Error message

Must not be null or whitespace

What it means

Thrown by Guard.ThrowIfNullOrWhitespace in the vendored StackExchangeRedis instrumentation's Guard helper when a required string parameter is null, empty, or whitespace-only. On .NET targets it delegates to ArgumentException.ThrowIfNullOrWhiteSpace; otherwise it throws ArgumentException with "Must not be null or whitespace". Stricter than 2048: blank strings like " " also fail.

Solutions

1. Trim and validate the value with string.IsNullOrWhiteSpace before passing it; provide a real value.
2. Correct the upstream configuration or input source so the field cannot be blank.
3. Add whitespace validation at your own boundary to fail with a more descriptive message.

Example fix

// before
UseKey(settings["Key"] ?? "   ");

// after
var key = settings["Key"]?.Trim();
ArgumentException.ThrowIfNullOrWhiteSpace(key);
UseKey(key);

if (string.IsNullOrWhiteSpace(name))
{
    throw new ArgumentException("Must not be null or whitespace", nameof(name));
}

static bool IsValidName([NotNullWhen(true)] string? name) => !string.IsNullOrWhiteSpace(name);

try
{
    instrumented.SetName(name);
}
catch (ArgumentException ex) when (ex.ParamName == "name")
{
    logger.LogError(ex, "'name' is required and must not be blank");
}

When it happens

Trigger: Passing a null, empty, or whitespace-only string to any API guarded by ThrowIfNullOrWhitespace, e.g. a name, key, or identifier derived from config or user input that contained only spaces.

Common situations: Config entries with placeholder spaces; trim operations that emptied the string; templates where a required field was left as blank/whitespace filler.

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 whitespace
• Must not be null
• Must not be null or empty
• Error message cannot be null or empty.

AI-assisted analysis of microsoft/aspire@25830f84bd (2026-09-16). Data as JSON: /api/errors/bdeecad419b7d5ff. Report an issue: GitHub.

Appendix: source

Thrown at src/Vendoring/OpenTelemetry.Instrumentation.StackExchangeRedis/Shared/Guard.cs:109

        }
#pragma warning restore CS8777 // Parameter must have a non-null value when exiting.

        /// <summary>
        /// Throw an exception if the value is null or whitespace.
        /// </summary>
        /// <param name="value">The value to check.</param>
        /// <param name="paramName">The parameter name to use in the thrown exception.</param>
        [DebuggerHidden]
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static void ThrowIfNullOrWhitespace([NotNull] string? value, [CallerArgumentExpression(nameof(value))] string? paramName = null)
#pragma warning disable CS8777 // Parameter must have a non-null value when exiting.
        {
#if NET
            ArgumentException.ThrowIfNullOrWhiteSpace(value, paramName);
#else
            if (string.IsNullOrWhiteSpace(value))
            {
                throw new ArgumentException("Must not be null or whitespace", paramName);
            }
#endif
        }
#pragma warning restore CS8777 // Parameter must have a non-null value when exiting.

        /// <summary>
        /// Throw an exception if the value is zero.
        /// </summary>
        /// <param name="value">The value to check.</param>
        /// <param name="message">The message to use in the thrown exception.</param>
        /// <param name="paramName">The parameter name to use in the thrown exception.</param>
        [DebuggerHidden]
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static void ThrowIfZero(int value, string message = "Must not be zero", [CallerArgumentExpression(nameof(value))] string? paramName = null)
        {
#if NET
            ArgumentOutOfRangeException.ThrowIfZero(value, paramName);
#else

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