argoproj/argo-workflows · error

malformed workflow template parameter "%s": valueFrom is nil

Error message

malformed workflow template parameter "%s": valueFrom is nil

What it means

Each parameter under the binding's `spec.submit.arguments.parameters` must set `valueFrom.event` (an expr expression evaluated against the event payload). This error fires when a parameter has no valueFrom at all, meaning the dispatcher has nothing to evaluate, so submission is aborted before the workflow is created. It is a WorkflowEventBinding spec validation gap caught at dispatch time.

Source

Thrown at server/event/dispatch/operation.go:147

		o.instanceIDService.Label(wf)
		err = o.populateWorkflowMetadata(wf, &submit.ObjectMeta)
		if err != nil {
			return nil, err
		}

		if wf.Name == "" {
			wf.SetName(wf.GetGenerateName() + util.RandSuffix())
		}

		// users will always want to know why a workflow was submitted,
		// so we label with creator (which is a standard) and the name of the triggering event
		//nolint: contextcheck
		creator.LabelCreator(o.ctx, wf)
		labels.Label(wf, common.LabelKeyWorkflowEventBinding, wfeb.Name)
		if submit.Arguments != nil {
			for _, p := range submit.Arguments.Parameters {
				if p.ValueFrom == nil {
					return nil, fmt.Errorf("malformed workflow template parameter \"%s\": valueFrom is nil", p.Name)
				}
				program, compileErr := expr.Compile(p.ValueFrom.Event, expr.Env(o.env))
				if compileErr != nil {
					return nil, fmt.Errorf("failed to compile workflow template parameter %s expression: %w", p.Name, compileErr)
				}
				result, runErr := expr.Run(program, o.env)
				if runErr != nil {
					return nil, fmt.Errorf("failed to evaluate workflow template parameter \"%s\" expression: %w", p.Name, runErr)
				}
				data, marshalErr := json.Marshal(result)
				if marshalErr != nil {
					return nil, fmt.Errorf("failed to convert result to JSON \"%s\" expression: %w", p.Name, marshalErr)
				}
				wf.Spec.Arguments.Parameters = append(wf.Spec.Arguments.Parameters, wfv1.Parameter{Name: p.Name, Value: wfv1.AnyStringPtr(wfv1.Item{Value: data})})
			}
		}
		wf, err = client.ArgoprojV1alpha1().Workflows(wfeb.Namespace).Create(ctx, wf, metav1.CreateOptions{})
		if err != nil {

View on GitHub (pinned to 35bff19146)

Solutions

1. Add a valueFrom with an event expression to the parameter: `parameters: [{name: msg, valueFrom: {event: '"hello"'}}]`.
2. If a static value was intended, note event bindings only support valueFrom.event; embed the constant as a string expression like `valueFrom: {event: "'my-static-value'"}`.
3. Check YAML indentation so `event:` is nested under `valueFrom:`.
4. Test the binding with `argo submit --from eventbinding/<name>` or the event API and confirm no `WorkflowEventBindingError` event appears.

Example fix

// before
parameters:
  - name: message
// after
parameters:
  - name: message
    valueFrom:
      event: '"static message"'

// every submit.arguments.parameters entry must set valueFrom.event
for _, p := range wfeb.Spec.Submit.Arguments.Parameters {
    if p.ValueFrom == nil || p.ValueFrom.Event == "" {
        return fmt.Errorf("parameter %q must set valueFrom.event", p.Name)
    }
}

When it happens

Trigger: A WorkflowEventBinding declares submit.arguments.parameters with only `name` (no `valueFrom:`), or valueFrom was dropped/omitted in YAML (e.g. wrong indentation nesting valueFrom under the wrong key). Dispatch of a matching event then fails for every such parameter.

Common situations: Copy-paste from a plain Workflow example where parameters carry static `value:`; YAML indentation error nesting `event:` outside `valueFrom`; hand-editing the binding CR and deleting the valueFrom block; schema validation not enforcing this at apply time (CRD allows it).

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.

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• CodeBadRequest
• failed to compile workflow template parameter %s expression:
• requested configuration is invalid: %w
• duplicate synchronization item found
• unable to parse node field selector '%s': %w

AI-assisted analysis of argoproj/argo-workflows@35bff19146 (2026-09-03). Data as JSON: /api/errors/4bc4d83a64e1d448. Report an issue: GitHub.