unoplatform/uno · error · ArgumentNullException

typeName

Error message

typeName

What it means

Thrown by XamlTypeName.TryParse when the `typeName` argument is null. TryParse is the core parser; a null input string has no characters to tokenize, so it rejects immediately rather than producing a misleading false return.

Source

Thrown at src/SourceGenerators/System.Xaml/System.Xaml.Schema/XamlTypeName.cs:45

using System.Linq;

namespace Uno.Xaml.Schema
{
	[UnconditionalSuppressMessage("Trimming", "IL2026", Justification = "Types manipulated here have been marked earlier")]
	public class XamlTypeName
	{
		public static XamlTypeName Parse (string typeName, IXamlNamespaceResolver namespaceResolver)
		{
			XamlTypeName n;
			if (!TryParse (typeName, namespaceResolver, out n))
				throw new FormatException (String.Format (CultureInfo.InvariantCulture, "Invalid typeName: '{0}'", typeName));
			return n;
		}

		public static bool TryParse (string typeName, IXamlNamespaceResolver namespaceResolver, out XamlTypeName result)
		{
			if (typeName == null)
				throw new ArgumentNullException ("typeName");
			if (namespaceResolver == null)
				throw new ArgumentNullException ("namespaceResolver");

			result = null;
			IList<XamlTypeName> args = null;
			int nArray = 0;
			int idx;

			if (typeName.Length > 2 && typeName [typeName.Length - 1] == ']') {
				idx = typeName.LastIndexOf ('[');
				if (idx < 0)
					return false; // mismatch brace
				nArray = 1;
				for (int i = idx + 1; i < typeName.Length - 1; i++) {
					if (typeName [i] != ',')
						return false; // only ',' is expected
					nArray++;
				}

View on GitHub (pinned to 0418340488)

Solutions

1. Null-check the input before calling TryParse and treat null as 'no type' in your flow.
2. Provide a default/empty string and let TryParse return false instead.
3. Validate upstream sources of the type-name string to ensure they are non-null.

Example fix

// before
XamlTypeName.TryParse(typeNameStr, resolver, out var name);

// after
if (typeNameStr == null) { name = null; return; }
XamlTypeName.TryParse(typeNameStr, resolver, out name);

// before TryParse
if (typeName == null) { result = null; return; }

When it happens

Trigger: Calling XamlTypeName.TryParse(null, resolver, out _); propagating a null type-name string from upstream (e.g. a missing attribute value, an empty element treated as a type reference).

Common situations: Config/code paths that read a type-name string from an optional attribute that was absent (null); deserialization feeding null into type resolution; unguarded string handling.

Related errors

• namespaceResolver
• typeNameList
• Invalid typeName: '{0}'
• Invalid type name list: '{0}'
• prefixLookup

AI-assisted analysis of unoplatform/uno@0418340488 (2026-08-13). Data as JSON: /api/errors/0504da2141a157f3. Report an issue: GitHub.