Only using unset apps and unset config together will do the expected unset apps' job

[MonicaisHer]

set app, unset apps, does not work:

$ sudo snap set edgex-device-mqtt apps.device-mqtt.config.service.port=1111
$ sudo snap restart edgex-device-mqtt.device-mqtt

$ sudo snap unset edgex-device-mqtt apps.device-mqtt.config.service.port
$ sudo snap restart edgex-device-mqtt.device-mqtt

$ snap get edgex-device-mqtt -d
{
    "apps": {
        "device-mqtt": {
            "config": {
                "service": {
                    "port": 1111
                }
            }
        }
    }
}
$ journalctl -f | grep device-mqtt |grep "Web server starting"
msg="Web server starting (localhost:1111)"

set app, unset apps and config, work as expected:

$ sudo snap set edgex-device-mqtt apps.device-mqtt.config.service.port=1111
$ sudo snap restart edgex-device-mqtt.device-mqtt

$ sudo snap unset edgex-device-mqtt apps.device-mqtt.config.service.port
$ sudo snap unset edgex-device-mqtt config.service.port
$ sudo snap restart edgex-device-mqtt.device-mqtt

$ snap get edgex-device-mqtt -d
{}
$ journalctl -f | grep device-mqtt |grep "Web server starting"
msg="Web server starting (localhost:59982)" <----------------------------------------default service port

See more details in this PR

[farshidtz]

This is because the unset makes the config object empty and as a result the env file never gets emptied:

edgex-snap-hooks/options/options.go

Lines 59 to 62 in 7fdbcd4

	if options.Config == nil {
	log.Debugf("No global configuration settings")
	return nil
	}

[farshidtz]

Fixed by #41