temporalio/temporal · error

history is nil

Error message

history is nil

What it means

pollTask polls a workflow task and expects the PollWorkflowTaskQueueResponse to carry a History. A nil history means the server returned a task without an execution history, which the test poller treats as unusable. This is a defensive guard so the helper fails with a clear message instead of nil-dereferencing history.Events.

Source

Thrown at common/testing/taskpoller/taskpoller.go:368

	}
	if req.TaskQueue == nil {
		req.TaskQueue = opts.tv.TaskQueue()
	}
	if req.Identity == "" {
		req.Identity = opts.tv.WorkerIdentity()
	}
	resp, err := p.client.PollWorkflowTaskQueue(ctx, req)
	if err != nil {
		return nil, err
	}
	if resp == nil || resp.TaskToken == nil {
		return nil, NoWorkflowTaskAvailable
	}

	var events []*historypb.HistoryEvent
	history := resp.History
	if history == nil {
		return nil, errors.New("history is nil")
	}

	events = history.Events
	if len(events) == 0 && req.TaskQueue.GetKind() != enumspb.TASK_QUEUE_KIND_STICKY {
		return nil, errors.New("history events are empty")
	}

	nextPageToken := resp.NextPageToken
	for nextPageToken != nil {
		resp, err := p.client.GetWorkflowExecutionHistory(
			ctx,
			&workflowservice.GetWorkflowExecutionHistoryRequest{
				Namespace:     p.namespace,
				Execution:     resp.WorkflowExecution,
				NextPageToken: nextPageToken,
			})
		if err != nil {
			return nil, err

View on GitHub (pinned to bde624efd1)

Solutions

  1. Ensure the mocked PollWorkflowTaskQueueResponse populates History with at least the WorkflowExecutionStarted event
  2. Verify the workflow is started before polling (StartWorkflow and wait for the first task)
  3. If polling a sticky task queue, set Kind: enumspb.TASK_QUEUE_KIND_STICKY so the empty-history path is allowed

Example fix

// before
resp, _ := poller.Poll(...) // fake client returns empty response
// after
resp, _ := poller.Poll(...)
require.NotNil(t, resp.History)
require.NotEmpty(t, resp.History.Events)
Defensive patterns

Strategy: validation

Validate before calling

if resp == nil || resp.History == nil {
    return errors.New("poll response has no history")
}

Try / catch

task, err := poller.PollForWorkflowTask(...)
if err != nil {
    // includes "history is nil"; inspect mock client's PollWorkflowTaskQueueResponse
}

Prevention

When it happens

Trigger: PollWorkflowTask/withHeaders returns a response whose History field is nil — typically a stubbed/fake client returning an empty PollWorkflowTaskQueueResponse, or an unexpected server response.

Common situations: Using TaskPoller against a mocked frontend client that forgot to populate resp.History; calling pollTask on a workflow that has not started so no history exists.

Related errors

AI-assisted analysis of temporalio/temporal@bde624efd1 (2026-09-01). Data as JSON: /api/errors/b79f3e6585fcad3f. Report an issue: GitHub.