dotnet/wpf · error · ArgumentException

SR.Format(SR.ValueInArrayIsNull, "types")

Error message

SR.Format(SR.ValueInArrayIsNull, "types")

What it means

GetFirstAmbientValue validates that no entry in the 'types' array is null before delegating to the inner context. A null XamlType element throws ArgumentException with ValueInArrayIsNull naming 'types'.

Solutions

  1. Filter null entries: types.Where(t => t != null).ToArray() before the call.
  2. Verify each SchemaContext.GetType/GetXamlType result for null before adding it to the array.
  3. Throw or log a specific message when a type fails to resolve so the bad source is identified.
  4. Catch ArgumentException to surface which ceiling-type list was malformed.

Example fix

// before
var ceiling = new[] { sxCtx.GetType(typeof(Grid)), sxCtx.GetType(typeof(Unknown)) };
var v = ambient.GetFirstAmbientValue(ceiling); // throws if second is null
// after
var ceiling = new[] { sxCtx.GetType(typeof(Grid)), sxCtx.GetType(typeof(Unknown)) }
    .Where(t => t != null).ToArray();
var v = ambient.GetFirstAmbientValue(ceiling);
Defensive patterns

Strategy: validation

Validate before calling

if (types.Any(t => t == null)) throw new ArgumentException("types contains null entries", nameof(types));

Type guard

XamlType[] NonNull(XamlType[] src) => src.Where(t => t != null).ToArray();

Try / catch

try { return ambient.GetFirstAmbientValue(types); }
catch (ArgumentException ex) { // null type entry
  throw new ArgumentException("Bad ceiling types array", ex); }

Prevention

When it happens

Trigger: Calling IAmbientProvider.GetFirstAmbientValue(types) where the types array contains a null element, e.g. GetFirstAmbientValue(new XamlType[] { schemaContext.GetType(typeof(Grid)), null }).

Common situations: Populating ceiling types from SchemaContext.GetType(typeof(T)) calls that returned null for unregistered or renamed types; arrays assembled from config or reflection data with missing entries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/ef55d6d4bacb5555. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Xaml/Context/ServiceProviderContext.cs:155

                {
                    // we don't allow any property to be null
                    throw new ArgumentException(SR.Format(SR.ValueInArrayIsNull, "properties"));
                }
            }

            return _xamlContext.ServiceProvider_GetFirstAmbientValue(ceilingTypes, properties);
        }

        object IAmbientProvider.GetFirstAmbientValue(params XamlType[] types)
        {
            ArgumentNullException.ThrowIfNull(types);

            foreach (var type in types)
            {
                if (type is null)
                {
                    // we don't allow any type to be null
                    throw new ArgumentException(SR.Format(SR.ValueInArrayIsNull, "types"));
                }
            }

            return _xamlContext.ServiceProvider_GetFirstAmbientValue(types);
        }

        IEnumerable<AmbientPropertyValue> IAmbientProvider.GetAllAmbientValues(
                                                    IEnumerable<XamlType> ceilingTypes,
                                                    params XamlMember[] properties)
        {
            ArgumentNullException.ThrowIfNull(properties);

            foreach (var property in properties)
            {
                if (property is null)
                {
                    // we don't allow any property to be null
                    throw new ArgumentException(SR.Format(SR.ValueInArrayIsNull, "properties"));

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