dotnet/wpf · error

(no message - parameterless InvalidOperationException)

Error message

(no message - parameterless InvalidOperationException)

What it means

MarkupWriter's internal value serializer converts a Type value to its XML namespace-qualified string form, but throws a parameterless InvalidOperationException when the value passed in is not a Type. This is an internal invariant violation: the serializer was invoked with a value it was never designed to handle.

Solutions

  1. Inspect the object being serialized and ensure every property that flows through the type serializer contains a non-null System.Type instance
  2. Check for nulls earlier in the object graph before calling MarkupWriter
  3. Wrap serialization in try/catch to log the offending property path
  4. If serializing custom types, register a proper value serializer that handles your value type

Example fix

// before
var markup = MarkupWriter.GetObjectMarkup(obj); // obj.SomeTypeProperty == null
// after
if (obj.SomeTypeProperty == null)
    throw new InvalidOperationException("obj.SomeTypeProperty must be a Type before serialization");
var markup = MarkupWriter.GetObjectMarkup(obj);
Defensive patterns

Strategy: validation

Validate before calling

if (value is not Type t || t == null)
    throw new InvalidOperationException("Expected a System.Type value before MarkupWriter serialization");

Type guard

bool IsType(object v) => v is Type;

Try / catch

try { var markup = MarkupWriter.GetObjectMarkup(obj); }
catch (InvalidOperationException ex) { Log(ex); /* inspect obj graph for null/non-Type members */ }

Prevention

When it happens

Trigger: Calling MarkupWriter/MarkupObject serialization APIs (e.g. MarkupWriter.GetObjectMarkup) or the XAML serializer pipeline where a member's value is null or not a System.Type when ConvertToString is dispatched for the x:Type-like value serializer.

Common situations: Serializing an object graph whose property typed/declared as Type is actually null or holds a non-Type instance; custom markup extensions or value serializer plumbing feeding unexpected values into the writer.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/10b628963d060115. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Markup/Primitives/MarkupWriter.cs:1526

        private class TypeValueSerializer : ValueSerializer
        {
            private Scope _scope;

            public TypeValueSerializer(Scope scope)
            {
                _scope = scope;
            }

            public override bool CanConvertToString(object value, IValueSerializerContext context)
            {
                return true;
            }

            public override string ConvertToString(object value, IValueSerializerContext context)
            {
                Type type = value as Type;
                if (type == null)
                    throw new InvalidOperationException();
                string uri = _scope.MakeAddressable(type);
                string prefix = _scope.GetPrefixOf(uri);
                if (prefix == null || prefix == "")
                    return type.Name;
                else
                    return $"{prefix}:{type.Name}";
            }

            public override IEnumerable<Type> TypeReferences(object value, IValueSerializerContext context)
            {
                Type type = value as Type;
                if (type != null)
                    return new Type[] { type };
                else
                    return base.TypeReferences(value, context);
            }
        }

View on GitHub (pinned to 81131a70a4)