[NF] Create Senml Messages for Linksmart

Zway-Bot/Moduls/Senml.cs

@@ -27,7 +27,7 @@ namespace ZwayBot.Moduls {
         topic = "/senml/" + sensor.SenmlTopic();
         data = sensor.ToSenml();
       }
-      if (topic != "" && data != "") {
+      if (topic != "" && data != null && data != "") {
         this.mqtt.Send(topic, data);
         this.Update?.Invoke(this, new MqttEvent(topic, data));
       }