fix headewr

pkg/ruleEngine/nodes/rest_api_request_node.go

@@ -63,9 +63,12 @@ func (r *RestApiRequestNode) OnMessage(ctx ruleEngine.Context, message *protocol
 	for k, v := range message.MetaData {
 		headers[k] = v.(string)
 	}
-	for _, v := range r.config.Headers {
-		headers[v.Key] = v.Value
+	if r.config.Headers != nil {
+		for _, v := range r.config.Headers {
+			headers[v.Key] = v.Value
+		}
 	}
+
 	req, err := utils.NewRequest(r.config.Method, r.config.Url, []byte(body))
 	if err != nil {
 		server.Log.Error(err)