Cant update brightness

[verti4cal]

Hi, thanks for the addon!

Got a error when trying to change the brightness of my lamps.
Nothing changes and the following error occures in the logs:

ERROR  : RangeError: Invalid status code: undefined
    at ServerResponse.writeHead (_http_server.js:200:11)
    at ServerResponse.writeHead (/home/pi/mozilla-iot/gateway/node_modules/on-headers/index.js:55:19)
    at ServerResponse._implicitHeader (_http_server.js:191:8)
    at ServerResponse.end (/home/pi/mozilla-iot/gateway/node_modules/compression/index.js:103:14)
    at ServerResponse.send (/home/pi/mozilla-iot/gateway/node_modules/express/lib/response.js:221:10)
    at ./src/controllers/things_controller.js.ThingsController.put (/home/pi/mozilla-iot/gateway/build/webpack:/src/controllers/things_controller.js:241:1)
    at <anonymous>

Tested Lamps:
OSRAM - Classic A60 W clear - V1.05.10
Philips - LLC020 (Extended color light) - 5.90.1.20202

ON/OFF works fine.