unoplatform/uno · error · ArgumentNullException

typeName

Error message

typeName

What it means

Thrown by the TypeExtension(string typeName) constructor when null is passed. The constructor immediately assigns the argument to TypeName, so a null would leave the extension in an invalid state; the guard fails fast instead.

Source

Thrown at src/SourceGenerators/System.Xaml/System.Windows.Markup/TypeExtension.cs:45

using System.Reflection;
using Uno.Xaml.Schema;

namespace System.Windows.Markup
{
	[MarkupExtensionReturnType (typeof (Type))]
	[TypeConverter (typeof (TypeExtensionConverter))]
	// [System.Runtime.CompilerServices.TypeForwardedFrom (Consts.AssemblyPresentationFramework_3_5)]
	public class TypeExtension : MarkupExtension
	{
		public TypeExtension ()
		{
		}

		public TypeExtension (string typeName)
		{
			if (typeName == null)
			{
				throw new ArgumentNullException ("typeName");
			}

			TypeName = typeName;
		}

		public TypeExtension (Type type)
		{
			if (type == null)
			{
				throw new ArgumentNullException ("type");
			}

			Type = type;
		}

		[ConstructorArgument ("type")]
		[DefaultValue (null)]
		public Type Type { get; set; }

View on GitHub (pinned to 0418340488)

Solutions

1. Pass a non-null, assembly-qualified or namespace-qualified type name string.
2. Null-check the input before constructing: if (name != null) ext = new TypeExtension(name);.
3. Prefer the TypeExtension(Type) overload when you already have a System.Type instance.

Example fix

// before
string name = GetNameOrNull();
var ext = new TypeExtension(name); // throws if null

// after
string name = GetNameOrNull() ?? throw new InvalidOperationException("type name required");
var ext = new TypeExtension(name);

string name = ResolveTypeName() ?? throw new InvalidOperationException("type name required");
var ext = new TypeExtension(name);

static bool IsValidTypeName(string s) => !string.IsNullOrWhiteSpace(s);

When it happens

Trigger: Constructing new TypeExtension((string)null) directly, or via reflection/deserialization that resolves the string overload with a null argument.

Common situations: Code that builds TypeExtension from a nullable string without checking; XAML converters that pass through unresolved type-name bindings as null.

Related errors

• type
• serviceProvider
• Either TypeName or Type must be filled before calling Provid
• serviceProvider does not provide IXamlTypeResolver service.
• Type '{0}' is not resolved as a valid type by the type resol

AI-assisted analysis of unoplatform/uno@0418340488 (2026-08-13). Data as JSON: /api/errors/285314cda41c8f7f. Report an issue: GitHub.