TypeError: harmonyHub.off is not a function

[RoelVG]

TypeError: harmonyHub.off is not a function
    at HarmonyHubWS.configHandler (/home/roel/chromecast-harmony-watchdog/src/harmony.js:64:16)
    at emitOne (events.js:116:13)
    at HarmonyHubWS.emit (events.js:211:7)
    at HarmonyHubWS.parseMessage (/home/roel/chromecast-harmony-watchdog/node_modules/harmonyhubws/lib/HarmonyHubWS.js:110:26)
    at WebSocket.socket.on (/home/roel/chromecast-harmony-watchdog/node_modules/harmonyhubws/lib/HarmonyHubWS.js:75:22)
    at emitOne (events.js:116:13)
    at WebSocket.emit (events.js:211:7)
    at Receiver.receiverOnMessage (/home/roel/chromecast-harmony-watchdog/node_modules/ws/lib/websocket.js:789:20)
    at emitOne (events.js:116:13)
    at Receiver.emit (events.js:211:7)

I get this error when a device starts casting to the configured Chromecast.

Changing "off" to "on" fixes this, but I'm not sure if the logic there makes sense then with the callback being registered again?