dotnet/wpf · error · ArgumentException

SR.NullUri

Error message

SR.NullUri

What it means

CheckKnownNamespaces throws ArgumentException (SR.NullUri) when the knownNamespaces dictionary passed to XmlStreamStore's constructor contains a null key (a null namespace Uri). Known namespaces must all be valid, distinct Uris.

Solutions

  1. Remove null keys from the knownNamespaces dictionary before constructing the store.
  2. Substitute a valid namespace Uri for the null entry, or drop the entry entirely.
  3. Guard the input: if (knownNamespaces.Keys.Any(k => k == null)) throw/report before constructing.

Example fix

// before
var known = new Dictionary<Uri, IList<Uri>> { { null, null } };
var store = new XmlStreamStore(stream, known);

// after
var known = new Dictionary<Uri, IList<Uri>>();
known[new Uri("http://schemas.microsoft.com/windows/annotations/2003/11/base")] = null;
var store = new XmlStreamStore(stream, known);
Defensive patterns

Strategy: validation

Validate before calling

if (knownNamespaces == null || knownNamespaces.Keys.Any(k => k == null)) throw new ArgumentException("knownNamespaces contains a null Uri");

Type guard

bool HasNullKeys(Dictionary<Uri, IList<Uri>> map) => map == null || map.Keys.Any(k => k == null);

Try / catch

try { var store = new XmlStreamStore(stream, knownNamespaces); }
catch (ArgumentException ex) when (ex.ParamName == "knownNamespaces") { /* sanitize and retry */ }

Prevention

When it happens

Trigger: new XmlStreamStore(stream, knownNamespaces) where dictionary keys include null (e.g., built from data where a namespace lookup returned null); checked during CheckKnownNamespaces from LoadStream.

Common situations: Building the namespace map from configuration where a missing entry became null; deserializing a namespace list with a null element; copy-pasting a sample dictionary with placeholder null keys.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/a0f30b901f25b20c. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Annotations/Storage/XmlStreamStore.cs:782

        private void CheckKnownNamespaces(IDictionary<Uri, IList<Uri>> knownNamespaces)
        {
            if (knownNamespaces == null)
                return;

            IList<Uri> allNamespaces = new List<Uri>();

            //add AnnotationFramework namespaces
            foreach (Uri name in _predefinedNamespaces.Keys)
            {
                allNamespaces.Add(name);
            }

            //add external namespaces
            foreach (Uri knownNamespace in knownNamespaces.Keys)
            {
                if (knownNamespace == null)
                {
                    throw new ArgumentException(SR.NullUri, nameof(knownNamespaces));
                }
                if (allNamespaces.Contains(knownNamespace))
                {
                    throw new ArgumentException(SR.DuplicatedUri, nameof(knownNamespaces));
                }
                allNamespaces.Add(knownNamespace);
            }

            // check compatible namespaces
            foreach (KeyValuePair<Uri, IList<Uri>> item in knownNamespaces)
            {
                if (item.Value != null)
                {
                    foreach (Uri name in item.Value)
                    {
                        if (name == null)
                        {
                            throw new ArgumentException(SR.NullUri, nameof(knownNamespaces));

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