STOMP notifier unsubscribe method fails with "Cannot unsubscribe as no subscription exists for id undefined"

When subscribing, an id is assigned to each channel. However on line https://github.com/aerogear/aerogear-js/blob/master/src/notifier/adapters/stompws.js#L396 the passed channels are used and they don't have any id. There should be a mapping between the passed channels and the internal this.getChannels() which have the assigned id.