fix error

pkg/ruleEngine/nodes/mqtt_broker_node.go

@@ -102,8 +102,12 @@ type MeteData struct {
 func (M *MQTTBrokerNode) OnMessage(ctx ruleEngine.Context, message *protocol.Message) error {
 	if M.mqttClient.IsConnected() {
 		var meteData MeteData
-		meteData.VendorId = message.MetaData["vendor_id"].(string)
-		meteData.VendorId = message.MetaData["device_id"].(string)
+		if v, ok := message.MetaData["vendor_id"]; ok {
+			meteData.VendorId = v.(string)
+		}
+		if v, ok := message.MetaData["device_id"]; ok {
+			meteData.DeviceId = v.(string)
+		}
 		tpl, err := template.New("topic").Parse(defaultTopicTemp)
 		if err != nil {
 			return err