elsa-workflows/elsa-core · error · InvalidOperationException

Either ActivityTypeName or StimulusHash must be specified.

Error message

Either ActivityTypeName or StimulusHash must be specified.

What it means

DispatchStimulusCommandHandler dispatches a stimulus either by activity type name or by a precomputed stimulus hash. If neither ActivityTypeName nor StimulusHash is provided on the request, the handler cannot form a stimulus and throws InvalidOperationException.

Solutions

1. Provide ActivityTypeName (with any stimulus data) or a StimulusHash on the request before dispatching.
2. If you expected a hash, verify the upstream value that produced it (e.g. the bookmark's stimulus hash) is non-null and passed through.
3. Add request validation at the API boundary to reject empty dispatch requests with a clear message.

Example fix

// before
await mediator.SendAsync(new DispatchStimulusCommand());
// after
await mediator.SendAsync(new DispatchStimulusCommand { ActivityTypeName = "HttpEndpoint", Stimulus = stimulus });

if (string.IsNullOrEmpty(request.ActivityTypeName) && string.IsNullOrEmpty(request.StimulusHash))
    throw new ArgumentException("Either ActivityTypeName or StimulusHash must be specified.");

try { await mediator.SendAsync(command); } catch (InvalidOperationException ex) when (ex.Message.Contains("ActivityTypeName or StimulusHash")) { return BadRequest(ex.Message); }

When it happens

Trigger: Sending a dispatch stimulus request (e.g. via the API or an IDispatchStimulusCommand) with both ActivityTypeName and StimulusHash null/empty — e.g. a workflow caller forwarding a bookmark or payload that omitted both fields.

Common situations: API clients building the request payload manually and omitting fields; a null stimulus hash propagated from an upstream bookmark lookup that returned nothing; automation calling the endpoint with an empty body.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

• A workflow definition handle must be provided.
• The specified activity is not part of the workflow.
• Workflow definition not found.
• Drain already in progress; second invocation rejected
• Drain already completed in this generation; subsequent…

AI-assisted analysis of elsa-workflows/elsa-core@fe9217bdfa (2026-09-13). Data as JSON: /api/errors/83a8acd9bc784c8e. Report an issue: GitHub.

Appendix: source

Thrown at src/modules/Elsa.Workflows.Runtime/Handlers/DispatchStimulusCommandHandler.cs:27

public class DispatchStimulusCommandHandler(IStimulusSender stimulusSender) : ICommandHandler<DispatchStimulusCommand>
{
    public async Task<Unit> HandleAsync(DispatchStimulusCommand command, CancellationToken cancellationToken)
    {
        var request = command.Request;

        if (request.ActivityTypeName != null)
        {
            await stimulusSender.SendAsync(request.ActivityTypeName, request.Stimulus!, request.Metadata, cancellationToken);
            return Unit.Instance;
        }

        if (request.StimulusHash != null)
        {
            await stimulusSender.SendAsync(request.StimulusHash!, request.Metadata, cancellationToken);
            return Unit.Instance;
        }

        throw new InvalidOperationException("Either ActivityTypeName or StimulusHash must be specified.");
    }
}

View on GitHub (pinned to fe9217bdfa)