return err if the spec area is nil after unmashal for tfjob v1alpha2 (k…

…ubeflow#678)

pkg/controller.v2/informer.go

@@ -89,7 +89,7 @@ func tfJobFromUnstructured(obj interface{}) (*tfv1alpha2.TFJob, error) {
 	}
 	var tfjob tfv1alpha2.TFJob
 	err := runtime.DefaultUnstructuredConverter.FromUnstructured(un.Object, &tfjob)
-	if err != nil {
+	if err != nil || tfjob.Spec.TFReplicaSpecs == nil {
 		return &tfjob, errFailedMarshal
 	}
 	return &tfjob, nil