return exec.Controller instead of nil

Signed-off-by: Evan Hazlett <ejhazlett@gmail.com>

api/types/swarm/task.go

@@ -66,8 +66,10 @@ type TaskSpec struct {
 	// parameters have been changed.
 	ForceUpdate uint64
 
-	Runtime     RuntimeType `json:",omitempty"`
-	RuntimeData []byte      `json:",omitempty"`
+	Runtime RuntimeType `json:",omitempty"`
+	// TODO (ehazlett): this should be removed and instead
+	// use struct tags (proto) for the runtimes
+	RuntimeData []byte `json:",omitempty"`
 }
 
 // Resources represents resources (CPU/Memory).

daemon/cluster/convert/service.go

@@ -79,7 +79,7 @@ func serviceSpecFromGRPC(spec *swarmapi.ServiceSpec) (*types.ServiceSpec, error)
 
 	taskTemplate := taskSpecFromGRPC(spec.Task)
 
-	switch t := spec.Task.Runtime.(type) {
+	switch t := spec.Task.GetRuntime().(type) {
 	case *swarmapi.TaskSpec_Container:
 		containerConfig := t.Container
 		taskTemplate.ContainerSpec = containerSpecFromGRPC(containerConfig)

daemon/cluster/executor/container/executor.go

@@ -185,11 +185,11 @@ func (e *executor) Controller(t *api.Task) (exec.Controller, error) {
 	case *api.TaskSpec_Container:
 		c, err := newController(e.backend, t, secrets.Restrict(e.secrets, t))
 		if err != nil {
-			return nil, err
+			return ctlr, err
 		}
 		ctlr = c
 	default:
-		return nil, fmt.Errorf("unsupported runtime: %q", r)
+		return ctlr, fmt.Errorf("unsupported runtime: %q", r)
 	}
 
 	return ctlr, nil