icsharpcode/ILSpy · error · ArgumentNullException

handle

Error message

handle

What it means

ArgumentNullException(nameof(handle)) from DecompileExtension(EntityHandle) when handle.IsNil. EntityHandle is a struct, so this is the nil sentinel rather than a language null; the library surfaces it as ArgumentNullException to flag an unprovided argument.

Source

Thrown at ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs:1459

						}
						else if (parentTypeDef != null)
						{
							parentTypeDef = FindCommonDeclaringTypeDefinition(parentTypeDef, ev.DeclaringTypeDefinition);
						}
						break;
					default:
						throw new NotSupportedException(entity.Kind.ToString());
				}
				first = false;
			}
			RunTransforms(syntaxTree, decompileRun, parentTypeDef != null ? new SimpleTypeResolveContext(parentTypeDef) : new SimpleTypeResolveContext(typeSystem.MainModule));
			return syntaxTree;
		}

		public SyntaxTree DecompileExtension(EntityHandle handle)
		{
			if (handle.IsNil)
				throw new ArgumentNullException(nameof(handle));
			syntaxTree = new SyntaxTree();
			var namespaces = new HashSet<string>();
			RequiredNamespaceCollector.CollectNamespaces(handle, module, namespaces);
			var decompileRun = CreateDecompileRun(namespaces);

			switch (handle.Kind)
			{
				case HandleKind.TypeDefinition:
					ITypeDefinition typeDef = module.GetDefinition((TypeDefinitionHandle)handle);
					syntaxTree.Members.Add(DoDecompile(typeDef, decompileRun, new SimpleTypeResolveContext(typeDef), asExtension: true));
					RunTransforms(syntaxTree, decompileRun, new SimpleTypeResolveContext(typeDef));
					break;
				case HandleKind.MethodDefinition:
					IMethod methodDef = module.GetDefinition((MethodDefinitionHandle)handle);
					var extensionInfo = methodDef.ResolveExtensionInfo();
					Debug.Assert(extensionInfo != null);
					var memberInfo = extensionInfo.InfoOfExtensionMember((IMethod)methodDef.MemberDefinition).GetValueOrDefault();
					var subst = new TypeParameterSubstitution(memberInfo.ExtensionGroupingTypeParameters, null);

View on GitHub (pinned to 60c08fcb74)

Solutions

1. Check handle.IsNil before calling DecompileExtension.
2. Resolve the extension-member handle from a known-good source (ResolveExtensionInfo) and bail if nil.

Example fix

// before
var tree = decompiler.DecompileExtension(handle);

// after
if (handle.IsNil) throw new ArgumentNullException(nameof(handle));
var tree = decompiler.DecompileExtension(handle);

if (handle.IsNil) throw new ArgumentNullException(nameof(handle));
var tree = decompiler.DecompileExtension(handle);

When it happens

Trigger: Calling DecompileExtension(default(EntityHandle)) or with a handle obtained from a lookup that returned nil.

Common situations: A selected extension-member handle that failed to resolve; passing a handle read from an uninitialized struct field.

Related errors

• types contains null element
• definitions
• definitions contains null element
• HandleKind {handle.Kind} is not supported!
• Extension member {extMember} is not supported for decompilat

AI-assisted analysis of icsharpcode/ILSpy@60c08fcb74 (2026-08-13). Data as JSON: /api/errors/98a54e25e47feca2. Report an issue: GitHub.