What causes "Missing value for {name}." in dotnet/orleans?

Supply the missing argument immediately after the flag, e.g. `dotnet run -- --connection-string " "`.

dotnet/orleans · error · ArgumentException

Missing value for {name}.

Error message

Missing value for {name}.

What it means

Thrown by the sample's command-line parser GetOptionValue when a flag like --connection-string, --container, or --blob is the very last token on the command line, so there is no following token to use as its value. It is a hard input-validation failure in the Program.Main path that builds the run configuration.

Source

Thrown at samples/JournalingAzureBlobJson/JournalingAzureBlobJson/Program.cs:220

                ?? DefaultBlobName;

            var resetBlob = !args.Contains("--no-reset", StringComparer.OrdinalIgnoreCase);

            return new(connectionString, containerName, blobName, resetBlob);
        }

        private static string? GetOptionValue(string[] args, string name)
        {
            for (var i = 0; i < args.Length; i++)
            {
                if (!string.Equals(args[i], name, StringComparison.OrdinalIgnoreCase))
                {
                    continue;
                }

                if (i + 1 == args.Length)
                {
                    throw new ArgumentException($"Missing value for {name}.");
                }

                return args[i + 1];
            }

            return null;
        }
    }
}

public interface IJournaledSampleGrain : IGrainWithStringKey
{
    Task<JournaledSampleSummary> RunScenario();
    Task<JournaledSampleSummary> GetSummary();
    Task Deactivate();
}

public sealed class JournaledSampleGrain(

View on GitHub (pinned to fca799fa70)

Solutions

Supply the missing argument immediately after the flag, e.g. `dotnet run -- --connection-string "<Azure storage conn string>"`.
If you intended the flag to be optional, remove it entirely so the sample falls back to the AZURE_STORAGE_CONNECTION_STRING environment variable / default blob name.
Check your shell quoting: a value containing spaces must be quoted so it does not get split into separate args.

Example fix

// before
GetOptionValue(args, "--connection-string") // throws if --connection-string is last token

// after: always pair the flag with its value on the command line
dotnet run -- --connection-string "DefaultEndpointsProtocol=..." --container journaling

Defensive patterns

Strategy: validation

Validate before calling

// Validate flag/value pairing before delegating to GetOptionValue
for (var i = 0; i < args.Length - 1; i++)
    if (args[i].StartsWith("--") && args[i + 1].StartsWith("--"))
        Console.WriteLine($"Warning: flag {args[i]} may be missing its value.");

Type guard

null

Try / catch

null

Prevention

Always quote values containing spaces so the shell does not split them.
Keep flags adjacent to their values on the command line.
For optional flags, omit them entirely rather than leaving them dangling.

When it happens

Trigger: Invoking the sample as `dotnet run -- --connection-string` (or --container / --blob) with nothing after the flag. The loop finds the flag at index i, then i + 1 == args.Length is true, so it throws ArgumentException instead of returning null.

Common situations: Copy-pasting a command and truncating it; quoting a value that the shell then drops; moving the flag to the end of the line and forgetting its argument; passing a value that starts with -- which is technically accepted but often a mistake.

Related errors

AI-assisted analysis of dotnet/orleans@fca799fa70 (2026-08-13). Data as JSON: /api/errors/bd301b2f718cdb89. Report an issue: GitHub.