unoplatform/uno · error · ArgumentNullException

type

Error message

type

What it means

Thrown by the TypeExtension(Type type) constructor when a null Type is supplied. The constructor stores the argument into the Type property which ProvideValue returns directly, so a null would propagate; the check rejects it at the boundary.

Source

Thrown at src/SourceGenerators/System.Xaml/System.Windows.Markup/TypeExtension.cs:55

		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; }
		[DesignerSerializationVisibility (DesignerSerializationVisibility.Hidden)]
		public string TypeName { get; set; }

		public override object ProvideValue (IServiceProvider serviceProvider)
		{
			if (Type != null)
			{
				return Type;
			}

View on GitHub (pinned to 0418340488)

Solutions

1. Pass a concrete, non-null System.Type obtained via typeof() or a successful Type.GetType call.
2. Guard the type resolution result before constructing the extension.
3. Fall back to the string constructor with an assembly-qualified name when the Type is unavailable.

Example fix

// before
var t = Type.GetType("MyLib.Foo, MyLib");
var ext = new TypeExtension(t); // throws if getType returned null

// after
var t = Type.GetType("MyLib.Foo, MyLib") ?? throw new TypeLoadException("MyLib.Foo missing");
var ext = new TypeExtension(t);

Type t = ResolveType() ?? throw new TypeLoadException("type not found");
var ext = new TypeExtension(t);

static bool IsKnownType(Type t) => t != null && !t.IsGenericTypeDefinition || t != null;

When it happens

Trigger: Constructing new TypeExtension((Type)null), or passing a typeof() expression whose target could not be resolved at compile/runtime.

Common situations: Building a TypeExtension from a reflection lookup that returned null; platform-conditional code where a type may not exist on a target TFM.

Related errors

• typeName
• 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/c1469af50b01e247. Report an issue: GitHub.