microsoft/aspire · error · InvalidCastException

Cannot cast ' ' from ' ' to

Error message

Cannot cast '{paramName}' from '{value?.GetType().ToString() ?? "null"}' to '{typeof(T)}'

What it means

Guard.ThrowIfNotOfType<T> performs a cast and throws InvalidCastException when the supplied object is null or not assignable to T, with a message showing the parameter name, the runtime type, and the target type. It is used where the vendored instrumentation expects a strongly-typed payload (e.g. an object box previously stored).

Solutions

1. Verify the object's actual runtime type matches T before the call (use `is T`).
2. Fix the code that stored the value so it stores the expected type.
3. Null-check the value before casting.
4. Check for version mismatches between packages that share the object contract.

Example fix

// before
var item = Guard.ThrowIfNotOfType<MyItem>(obj); // obj is actually OtherItem
// after
if (obj is MyItem item) { /* use item */ } else { /* handle mismatch */ }

if (value is not T) throw new InvalidCastException($"Expected {typeof(T)}, got {value?.GetType().Name ?? "null"}");

if (value is T typed) { /* use typed */ } else { /* handle mismatch */ }

catch (InvalidCastException ex) { log.LogError(ex, "payload type mismatch"); }

When it happens

Trigger: Calling Guard.ThrowIfNotOfType<T>(value) where value is null or of an unrelated type; typically when retrieving cached/state objects that were stored under a different type.

Common situations: Two different components storing different types under the same key; an object changed type after a library upgrade; null leaking into an expected non-null slot.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

• The specified value is not an Int32.
• A of type cannot be assigned to a BicepValue< >.
• aspire: dict getter returned unexpected type %T
• aspire: dict.toObject: unexpected result type %T
• Aspire.Hosting/Dict.toObject only supports string-key…

AI-assisted analysis of microsoft/aspire@25830f84bd (2026-09-16). Data as JSON: /api/errors/6a36452dbc1b4fa1. Report an issue: GitHub.

Appendix: source

Thrown at src/Vendoring/OpenTelemetry.Instrumentation.StackExchangeRedis/Shared/Guard.cs:209

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static void ThrowIfOutOfRange(double value, [CallerArgumentExpression(nameof(value))] string? paramName = null, double min = double.MinValue, double max = double.MaxValue, string? minName = null, string? maxName = null, string? message = null)
        {
            Range(value, paramName, min, max, minName, maxName, message);
        }

        /// <summary>
        /// Throw an exception if the value is not of the expected type.
        /// </summary>
        /// <param name="value">The value to check.</param>
        /// <param name="paramName">The parameter name to use in the thrown exception.</param>
        /// <typeparam name="T">The type attempted to convert to.</typeparam>
        /// <returns>The value casted to the specified type.</returns>
        [DebuggerHidden]
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static T ThrowIfNotOfType<T>([NotNull] object? value, [CallerArgumentExpression(nameof(value))] string? paramName = null)
        {
            return value is not T result
                ? throw new InvalidCastException($"Cannot cast '{paramName}' from '{value?.GetType().ToString() ?? "null"}' to '{typeof(T)}'")
                : result;
        }

        [DebuggerHidden]
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static void Range<T>(T value, string? paramName, T min, T max, string? minName, string? maxName, string? message)
            where T : IComparable<T>
        {
            if (value.CompareTo(min) < 0 || value.CompareTo(max) > 0)
            {
                var minMessage = minName != null ? $": {minName}" : string.Empty;
                var maxMessage = maxName != null ? $": {maxName}" : string.Empty;
                var exMessage = message ?? string.Format(
                    CultureInfo.InvariantCulture,
                    "Must be in the range: [{0}{1}, {2}{3}]",
                    min,
                    minMessage,
                    max,

View on GitHub (pinned to 25830f84bd)