icsharpcode/ILSpy · error · ArgumentException

definitions contains null element

Error message

definitions contains null element

What it means

ArgumentException from Decompile(IEnumerable<EntityHandle>) when the sequence contains a handle with IsNil == true (default(EntityHandle), token 0). Same guard as DecompileTypes but for the mixed entity (type/method/field/property/event) overload.

Source

Thrown at ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs:1375

		/// </summary>
		public SyntaxTree Decompile(params EntityHandle[] definitions)
		{
			return Decompile((IEnumerable<EntityHandle>)definitions);
		}

		/// <summary>
		/// Decompile the specified types and/or members.
		/// </summary>
		public SyntaxTree Decompile(IEnumerable<EntityHandle> definitions)
		{
			if (definitions == null)
				throw new ArgumentNullException(nameof(definitions));
			syntaxTree = new SyntaxTree();
			var namespaces = new HashSet<string>();
			foreach (var entity in definitions)
			{
				if (entity.IsNil)
					throw new ArgumentException("definitions contains null element");
				RequiredNamespaceCollector.CollectNamespaces(entity, module, namespaces);
			}
			var decompileRun = CreateDecompileRun(namespaces);

			bool first = true;
			ITypeDefinition? parentTypeDef = null;
			foreach (var entity in definitions)
			{
				switch (entity.Kind)
				{
					case HandleKind.TypeDefinition:
						ITypeDefinition typeDef = module.GetDefinition((TypeDefinitionHandle)entity);
						syntaxTree.Members.Add(DoDecompile(typeDef, decompileRun, new SimpleTypeResolveContext(typeDef)));
						if (first)
						{
							parentTypeDef = typeDef.DeclaringTypeDefinition;
						}
						else if (parentTypeDef != null)

View on GitHub (pinned to 60c08fcb74)

Solutions

1. Filter nil handles before the call: definitions.Where(h => !h.IsNil).
2. Validate: if (definitions.Any(h => h.IsNil)) throw ... with caller context.

Example fix

// before
var tree = decompiler.Decompile(handles);

// after
var valid = handles.Where(h => !h.IsNil).ToArray();
var tree = decompiler.Decompile(valid);

var valid = definitions.Where(h => !h.IsNil).ToArray();
var tree = decompiler.Decompile(valid);

static bool IsValidEntityHandle(EntityHandle h) => !h.IsNil;

When it happens

Trigger: A mixed EntityHandle collection built from multiple sources where one element is default(EntityHandle); merging handles without filtering the nil sentinel.

Common situations: Concatenating type + member handle lists where one lookup returned default; reading handles from an array with an empty slot.

Related errors

• types contains null element
• definitions
• handle
• Could not find type definition {fullTypeName} in type system
• HandleKind {handle.Kind} is not supported!

AI-assisted analysis of icsharpcode/ILSpy@60c08fcb74 (2026-08-13). Data as JSON: /api/errors/d81d399de479fd9d. Report an issue: GitHub.