unoplatform/uno · error · ArgumentNullException

arrayType

Error message

arrayType

What it means

ArgumentNullException thrown by ArrayExtension (System.Xaml, ported from Mono) when its ArrayExtension(Type arrayType) constructor is called with a null Type. This constructor sets the element type of the array to build; a null type is meaningless, so it is rejected with parameter name 'arrayType'.

Source

Thrown at src/SourceGenerators/System.Xaml/System.Windows.Markup/ArrayExtension.cs:59

			items = new ArrayList ();
		}

		public ArrayExtension (Array elements)
		{
			if (elements == null)
			{
				throw new ArgumentNullException ("elements");
			}

			Type = elements.GetType ().GetElementType ();
			items = new ArrayList (elements);
		}

		public ArrayExtension (Type arrayType)
		{
			if (arrayType == null)
			{
				throw new ArgumentNullException ("arrayType");
			}

			Type = arrayType;
			items = new ArrayList ();
		}

		[ConstructorArgument ("arrayType")]
		public Type Type { get; set; }

		IList items;
		[DesignerSerializationVisibility (DesignerSerializationVisibility.Content)]
		public IList Items {
			get { return items; }
		}

		public void AddChild (Object value)
		{
			// null is allowed.

View on GitHub (pinned to 0418340488)

Solutions

1. Resolve the Type before constructing and null-check it; surface a clear error if the type name cannot be resolved.
2. Use the parameterless constructor and set the Type property explicitly after validation.
3. Validate the type name string against loaded assemblies before Type.GetType.

Example fix

// before
var t = Type.GetType(configTypeName);
var ext = new ArrayExtension(t); // t may be null

// after
var t = Type.GetType(configTypeName)
    ?? throw new ConfigurationException($"Unknown array type '{configTypeName}'.");
var ext = new ArrayExtension(t);

static ArrayExtension ArrayExtOfType(string typeName) { var t = Type.GetType(typeName) ?? throw new ConfigurationException($"Unknown type '{typeName}'."); return new ArrayExtension(t); }

static bool IsResolvableType(string name) => Type.GetType(name) is not null;

try { return new ArrayExtension(t); } catch (ArgumentNullException ex) when (ex.ParamName == "arrayType") { throw new ConfigurationException("Array element type could not be resolved."); }

When it happens

Trigger: Programmatic construction 'new ArrayExtension((Type)null)' or a reflection/code-gen path where the type argument resolves to null (e.g. Type.GetType returning null for an unresolvable name).

Common situations: Type.GetType("UnknownType") yielding null passed in, a config-driven array-type name that fails to resolve, or unit tests constructing the extension without a concrete type.

Related errors

• elements
• Type property must be set before calling ProvideValue method
• Item in the array must be an instance of '{0}'
• serviceProvider
• serviceProvider

AI-assisted analysis of unoplatform/uno@0418340488 (2026-08-13). Data as JSON: /api/errors/6e12520ff8c113ad. Report an issue: GitHub.