title: RxJava(Kotlin), Observable.amb and PublishSubject is not firing
body: <p>We're trying to observe either a 15s interval, or whenever we're firing <code>onNext</code> on our subject <code>refreshEventsSubject</code>, but without success.</p>
  
  <p>The subject is initiated like so</p>
  
  <p><code>private val refreshEventsSubject = PublishSubject&lt;Long&gt;()</code></p>
  
  <p>And then we try to observe it like this</p>
  
  <p><code>Observable.merge(Observable.interval(0, 15, TimeUnit.SECONDS), refreshEventsSubject)
      .subscribe { ... }</code></p>
  
  <p>We get the events from the interval every 15s, but the subject is not firing after running</p>
  
  <p><code>refreshEventsSubject.onNext(0)</code></p>
  
  <p>Any ideas appreciated.</p>
  
  <p>(Everything is written in Kotlin)</p>