Fix incorrect nil handling in workflowTaskPoller (cadence-workflow#1412)

What changed?

explicit nil handling in newWorkflowTaskPoller for ldaTunnel
Why?

Golang doesn't handle passing in nil pointer of concrete type directly into the interface. It still considers it not nil, which will cause panic in this case.

How did you test it?

Unit test fail before and pass after the change

Author: shijiesheng

internal/internal_task_pollers.go

@@ -290,14 +290,22 @@ func newWorkflowTaskPoller(
 	domain string,
 	params workerExecutionParameters,
 ) *workflowTaskPoller {
+	/*
+		Explicit nil handling is needed here. Otherwise, poller.ldaTunnel would not return a nil result
+	*/
+	var ldaTunnelInterface localDispatcher
+	if ldaTunnel != nil {
+		ldaTunnelInterface = ldaTunnel
+	}
+
 	return &workflowTaskPoller{
 		basePoller:                   basePoller{shutdownC: params.WorkerStopChannel},
 		service:                      service,
 		domain:                       domain,
 		taskListName:                 params.TaskList,
 		identity:                     params.Identity,
 		taskHandler:                  taskHandler,
-		ldaTunnel:                    ldaTunnel,
+		ldaTunnel:                    ldaTunnelInterface,
 		metricsScope:                 metrics.NewTaggedScope(params.MetricsScope),
 		logger:                       params.Logger,
 		stickyUUID:                   uuid.New(),

internal/internal_task_pollers_test.go

@@ -46,6 +46,21 @@ const (
 	_testIdentity   = "test-worker"
 )
 
+func Test_newWorkflowTaskPoller(t *testing.T) {
+	t.Run("success with nil ldaTunnel", func(t *testing.T) {
+		poller := newWorkflowTaskPoller(
+			nil,
+			nil,
+			nil,
+			_testDomainName,
+			workerExecutionParameters{})
+		assert.NotNil(t, poller)
+		if poller.ldaTunnel != nil {
+			t.Error("unexpected not nil ldaTunnel")
+		}
+	})
+}
+
 func TestLocalActivityPanic(t *testing.T) {
 	// regression: panics in local activities should not terminate the process
 	s := WorkflowTestSuite{logger: testlogger.NewZap(t)}