icsharpcode/ILSpy · error · ArgumentNullException

error

Error message

error

What it means

Thrown by CSharpDecompiler.GetErrorHeadline(DecompilerException error): error == null -> throw new ArgumentNullException(nameof(error)). The message is the parameter name 'error'. GetErrorHeadline formats a one-line description of a decompiler failure and requires a real exception.

Source

Thrown at ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs:327

		/// <summary>
		/// The headline a front end puts above the list of failures it recovered from. Shared so the
		/// UI, the command line and any other consumer say the same thing and point at the same URL.
		/// </summary>
		public static IEnumerable<string> GetErrorSummaryLines(int errorCount)
		{
			yield return $"{errorCount} error(s) occurred; the affected code was replaced by the error text in the output.";
			yield return $"Please report them at {DecompilationErrorReportUrl}:";
		}

		/// <summary>
		/// The one-line description of a single failure, so the UI and the command line name it the
		/// same way.
		/// </summary>
		public static string GetErrorHeadline(DecompilerException error)
		{
			if (error == null)
				throw new ArgumentNullException(nameof(error));
			return error.InnerException == null ? error.Message : $"{error.Message}: {error.InnerException.Message}";
		}

		/// <summary>
		/// Renders <paramref name="error"/> as the lines of a comment block: an explanation, the
		/// request to report it, and the full exception including its stack trace, which is what
		/// makes such a report actionable.
		/// </summary>
		internal static IEnumerable<string> GetErrorCommentLines(Exception error)
		{
			yield return "ILSpy could not decompile this. Please report the exception below,";
			yield return "along with the assembly it came from, at " + DecompilationErrorReportUrl;
			foreach (string line in error.ToString().Split('\n'))
			{
				yield return line.TrimEnd('\r');
			}
		}

View on GitHub (pinned to 60c08fcb74)

Solutions

1. Pass a non-null DecompilerException to GetErrorHeadline.
2. Null-check the exception at the call site before formatting the headline.

Example fix

// before
var headline = CSharpDecompiler.GetErrorHeadline(maybeNullError);

// after
var headline = maybeNullError == null
    ? "Decompilation failed."
    : CSharpDecompiler.GetErrorHeadline(maybeNullError);

if (error == null) throw new ArgumentNullException(nameof(error));
var headline = CSharpDecompiler.GetErrorHeadline(error);

var headline = error != null
    ? CSharpDecompiler.GetErrorHeadline(error)
    : "Decompilation failed.";

When it happens

Trigger: Calling GetErrorHeadline(null) directly, or code that passed a null DecompilerException through to it.

Common situations: Internal/UI code path that obtained no exception object (e.g. a decompile list with a null entry) and forwarded it.

Related errors

• v
• typeSystem
• types
• Cannot use an uncached type system in the decompiler.
• Error decompiling module and assembly attributes of {module.

AI-assisted analysis of icsharpcode/ILSpy@60c08fcb74 (2026-08-13). Data as JSON: /api/errors/c0c9d76b1ca0091a. Report an issue: GitHub.