dotnet/wpf · error · ArgumentException

SR.ReferenceIsNull

Error message

SR.ReferenceIsNull

What it means

XamlSchemaContext.GetXamlType(XamlTypeName) validates that the type name's Name property is non-null before resolving. A XamlTypeName with a null Name cannot denote a type, so an ArgumentException naming the offending member is thrown.

Solutions

1. Ensure XamlTypeName is constructed with a non-null local name
2. Validate xamlTypeName.Name before calling GetXamlType
3. Use XamlTypeName.Parse with a well-formed 'prefix:localName' string

Example fix

// before
var xn = new XamlTypeName("http://schemas.microsoft.com/winfx/2006/xaml", null);
schemaContext.GetXamlType(xn);
// after
var xn = new XamlTypeName("http://schemas.microsoft.com/winfx/2006/xaml", "NullExtension");
schemaContext.GetXamlType(xn);

if (xamlTypeName is null || xamlTypeName.Name is null) throw new ArgumentException("xamlTypeName must have a Name");

bool HasName(XamlTypeName t) => t?.Name is not null;

try { var xt = ctx.GetXamlType(xtn); } catch (ArgumentException ex) when (ex.ParamName == "xamlTypeName") { /* handle missing Name */ }

When it happens

Trigger: Calling schemaContext.GetXamlType(new XamlTypeName(ns, null)) or passing a XamlTypeName constructed/parsed such that Name is null (e.g. default-constructed then partially filled).

Common situations: Manually building XamlTypeName instances; parsing prefix strings where the local-name portion was empty; refactoring code that previously supplied both namespace and name.

Related errors

• ArgumentNullException(nameof(assemblyName))
• ArgumentNullException(nameof(assemblyNames))
• ArgumentNullException(nameof(assemblyPath))
• ArgumentNullException(nameof(clrNamespace))
• ArgumentNullException(nameof(localName))

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/6511a40e6e482ba9. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Xaml/XamlSchemaContext.cs:279

            if (XamlLanguage.XamlNamespaces.Contains(xamlNamespace))
            {
                return XamlLanguage.LookupXamlDirective(name);
            }
            else if (XamlLanguage.XmlNamespaces.Contains(xamlNamespace))
            {
                return XamlLanguage.LookupXmlDirective(name);
            }

            return null;
        }

        public XamlType GetXamlType(XamlTypeName xamlTypeName)
        {
            ArgumentNullException.ThrowIfNull(xamlTypeName);
            if (xamlTypeName.Name is null)
            {
                throw new ArgumentException(SR.Format(SR.ReferenceIsNull, "xamlTypeName.Name"), nameof(xamlTypeName));
            }

            if (xamlTypeName.Namespace is null)
            {
                throw new ArgumentException(SR.Format(SR.ReferenceIsNull, "xamlTypeName.Namespace"), nameof(xamlTypeName));
            }

            XamlType[] typeArgs = null;
            if (xamlTypeName.HasTypeArgs)
            {
                typeArgs = new XamlType[xamlTypeName.TypeArguments.Count];
                for (int i = 0; i < xamlTypeName.TypeArguments.Count; i++)
                {
                    if (xamlTypeName.TypeArguments[i] is null)
                    {
                        throw new ArgumentException(SR.Format(SR.CollectionCannotContainNulls, "xamlTypeName.TypeArguments"));
                    }

View on GitHub (pinned to 81131a70a4)