I tried recreating the issue you described here, where the Device: Get node returns
null for applications with multiple devices, but haven’t been able to do so.
Regarding the “Ammonia Sensor” application, the screenshot you provided is actually for the “Device State” output node, not the “Device: Get” data node. So I took a look in your account and in that application, your workflow is querying for the device tag “sigfox_id2”. Only one of the two devices in that application has such a tag (the other has a “sigfox_id” tag). So if you were trying to retrieve the device matching the Sigfox ID of the device with the “sigfox_id” tag, that would explain the
null response as no devices match the query.
In the case of the “Room Occupancy” application, your “Device: Get” node is actually configured correctly but the “Device State” node that follows it isn’t actually using the result of that query, as it is setting state values for a specific device in your application and not the device that is the result of the query.
To guard against the case where there is no device matching the Sigfox ID you provide, you will want to use a Conditional Node after your Device: Get node to confirm that a device matching the query was found. Otherwise you will get the “Invalid Device ID” error and the workflow will stop at that point.