allow nil/unversioned ramping version if current version is already nil/unversioned and ramp percentage is 0

service/worker/workerdeployment/workflow.go

@@ -409,7 +409,8 @@ func (d *WorkflowRunner) validateStateBeforeAcceptingRampingUpdate(args *deploym
 		return temporal.NewApplicationError("conflict token mismatch", errFailedPrecondition)
 	}
 	//nolint:staticcheck // SA1019: worker versioning v0.31
-	if args.Version == d.State.GetRoutingConfig().GetCurrentVersion() {
+	if args.Version == d.State.GetRoutingConfig().GetCurrentVersion() &&
+		!(args.Version == worker_versioning.UnversionedVersionId && args.Percentage == 0) {
 		d.logger.Info("version can't be set to ramping since it is already current")
 		return temporal.NewApplicationError(fmt.Sprintf("requested ramping version %s is already current", args.Version), errFailedPrecondition)
 	}
@@ -908,14 +909,17 @@ func (d *WorkflowRunner) syncVersion(ctx workflow.Context, targetVersion string,
 func (d *WorkflowRunner) syncUnversionedRamp(ctx workflow.Context, versionUpdateArgs *deploymentspb.SyncVersionStateUpdateArgs) error {
 	activityCtx := workflow.WithActivityOptions(ctx, defaultActivityOptions)
 
-	// DescribeVersion activity to get all the task queues in the current version
+	// DescribeVersion activity to get all the task queues in the current version, or the ramping version if current is nil
+	version := d.State.RoutingConfig.CurrentVersion //nolint:staticcheck // SA1019: worker versioning v0.31
+	if version == worker_versioning.UnversionedVersionId {
+		version = d.State.RoutingConfig.RampingVersion //nolint:staticcheck // SA1019: worker versioning v0.31
+	}
 	var res deploymentspb.DescribeVersionFromWorkerDeploymentActivityResult
 	err := workflow.ExecuteActivity(
 		activityCtx,
 		d.a.DescribeVersionFromWorkerDeployment,
 		&deploymentspb.DescribeVersionFromWorkerDeploymentActivityArgs{
-			Version: d.State.RoutingConfig.CurrentVersion, //nolint:staticcheck // SA1019: worker versioning v0.31
-
+			Version: version,
 		}).Get(ctx, &res)
 	if err != nil {
 		return err

tests/worker_deployment_test.go

@@ -967,6 +967,23 @@ func (s *WorkerDeploymentSuite) TestSetWorkerDeploymentRampingVersion_Invalid_Se
 	})
 }
 
+func (s *WorkerDeploymentSuite) TestSetWorkerDeploymentRampingVersion_Valid_SetNilCurrent_To_Ramping() {
+	ctx, cancel := context.WithTimeout(context.Background(), time.Minute)
+	defer cancel()
+
+	tv := testvars.New(s).WithBuildIDNumber(1)
+	s.startVersionWorkflow(ctx, tv)
+
+	s.setAndVerifyRampingVersion(ctx, tv, false, 5, false, "", &workflowservice.SetWorkerDeploymentRampingVersionResponse{})
+
+	// should be able to unset ramping version while current version is nil with no error
+	s.setAndVerifyRampingVersion(ctx, tv, true, 0, true, "", &workflowservice.SetWorkerDeploymentRampingVersionResponse{
+		PreviousVersion:           tv.DeploymentVersionString(), //nolint:staticcheck // SA1019: worker versioning v0.31
+		PreviousDeploymentVersion: tv.ExternalDeploymentVersion(),
+		PreviousPercentage:        5,
+	})
+}
+
 func (s *WorkerDeploymentSuite) TestSetWorkerDeploymentRampingVersion_ModifyExistingRampVersionPercentage() {
 	ctx, cancel := context.WithTimeout(context.Background(), time.Minute)
 	defer cancel()
@@ -1140,7 +1157,7 @@ func (s *WorkerDeploymentSuite) TestSetWorkerDeploymentRampingVersion_WithCurren
 			Name:       tv.DeploymentSeries(),
 			CreateTime: versionCreateTime,
 			RoutingConfig: &deploymentpb.RoutingConfig{
-				RampingVersion:                      "",
+				RampingVersion:                      worker_versioning.UnversionedVersionId, //nolint:staticcheck // SA1019: worker versioning v0.31
 				RampingVersionPercentage:            0,
 				RampingVersionChangedTime:           unsetRampingUpdateTime,
 				RampingVersionPercentageChangedTime: unsetRampingUpdateTime,
@@ -2853,7 +2870,7 @@ func (s *WorkerDeploymentSuite) setAndVerifyRampingVersionUnversionedOption(
 		version = worker_versioning.UnversionedVersionId
 	}
 	if unset {
-		version = ""
+		version = worker_versioning.UnversionedVersionId
 		percentage = 0
 	}
 	if !unversioned && !unset {