do not send alerts when there are no metrics

check_nodes/main.go

@@ -284,6 +284,8 @@ func vbat2percent(vbat string) int {
 func getLastMetrics(deveui string) OneMetric {
 	var res OneMetric
 
+	res.BatteryPercent = "999"
+
 	url := "http://localhost:8086/api/v2/query?org=wobischorg"
 	data := []byte(fmt.Sprintf(`from(bucket:"wobischbucket") 
                                  |> range(start:-5d)