dotnet/wpf · error · ArgumentException

SR.ReferenceIsNull (item.Key)

Error message

SR.ReferenceIsNull (item.Key)

What it means

NameScope.Add(KeyValuePair<string,object>) throws ArgumentException(SR.ReferenceIsNull) when the pair's Key or Value is null. A namescope entry needs both a non-null name and a non-null scoped object.

Solutions

1. Ensure item.Key is a non-empty-safe, non-null string before Add (Value must also be non-null).
2. Filter out null-keyed/null-valued pairs before adding.
3. Use RegisterName which gives clearer validation messages.

Example fix

// before
scope.Add(new KeyValuePair<string, object>(name, element)); // name may be null
// after
if (name != null && element != null) scope.Add(new KeyValuePair<string, object>(name, element));

if (item.Key == null || item.Value == null) throw new ArgumentException("item", "Key and Value must be non-null");

bool IsValidPair(KeyValuePair<string, object> p) => p.Key != null && p.Value != null;

try { nameScope.Add(item); } catch (ArgumentException ex) when (ex.ParamName == "item") { /* skip or fix the null-keyed pair */ }

When it happens

Trigger: Adding a KeyValuePair<string,object> whose Key is null (or Value is null) via the ICollection<KVP> Add implementation, e.g. from LINQ or collection-initializer code with null entries.

Common situations: Dictionary enumerations that include null keys, data-binding or test code constructing pairs from nullable sources.

Related errors

• ArgumentNullException(nameof(arrayType))
• ArgumentNullException(nameof(clrNamespace))
• ArgumentNullException(nameof(contentType))
• ArgumentNullException(nameof(loaderType))
• ArgumentNullException(nameof(member))

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/b5d042aec4ccec41. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Xaml/NameScope.cs:145

        {
            if (!Contains(item))
            {
                return false;
            }

            if (item.Value != this[item.Key])
            {
                return false;
            }

            return Remove(item.Key);
        }

        public void Add(KeyValuePair<string, object> item)
        {
            if (item.Key is null)
            {
                throw new ArgumentException(SR.Format(SR.ReferenceIsNull, "item.Key"), nameof(item));
            }

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

            Add(item.Key, item.Value);
        }

        public bool Contains(KeyValuePair<string, object> item)
        {
            if (item.Key is null)
            {
                throw new ArgumentException(SR.Format(SR.ReferenceIsNull, "item.Key"), nameof(item));
            }

            return ContainsKey(item.Key);

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