Merge pull request #138 from fangyincheng/master

Fix: check service.Group and service.Interface
diff --git a/request.go b/request.go
index 968372d..27437c6 100644
--- a/request.go
+++ b/request.go
@@ -236,10 +236,13 @@
 	}
 
 	request.Attachments[PATH_KEY] = service.Path
-	request.Attachments[GROUP_KEY] = service.Group
-	request.Attachments[INTERFACE_KEY] = service.Interface
 	request.Attachments[VERSION_KEY] = service.Version
-
+	if len(service.Group) > 0 {
+		request.Attachments[GROUP_KEY] = service.Group
+	}
+	if len(service.Interface) > 0 {
+		request.Attachments[INTERFACE_KEY] = service.Interface
+	}
 	if service.Timeout != 0 {
 		request.Attachments[TIMEOUT_KEY] = strconv.Itoa(int(service.Timeout / time.Millisecond))
 	}