crash on disabling speakers

[gretel]

/home/tom/node_modules/airtunes/lib/rtsp.js:385
    this.socket.end(this.makeHead('TEARDOWN', '', di) + '\r\n');
                ^

TypeError: Cannot read property 'end' of null
    at Client.sendNextRequest (/home/tom/node_modules/airtunes/lib/rtsp.js:385:17)
    at Client.teardown (/home/tom/node_modules/airtunes/lib/rtsp.js:124:8)
    at AirTunesDevice.stop (/home/tom/node_modules/airtunes/lib/device_airtunes.js:121:13)
    at stop (/home/tom/node_modules/airtunes2mqtt/index.js:250:30)
    at Socket.client.on.data (/home/tom/node_modules/airtunes2mqtt/index.js:369:17)
    at Socket.emit (events.js:182:13)
    at /home/tom/node_modules/socket.io/lib/socket.js:528:12
    at process._tickCallback (internal/process/next_tick.js:61:11)