title: RxJava3. Why FlowableSubscriber onNext has not been called?
body: <p>I need to get a Subscription object to have an opportunity of unsubscribing listeners. For this I want to give a FlowableSubscriber to function.</p>
  <p>Code:</p>
  <pre><code>FlowableSubscriber fs = new FlowableSubscriber() {
          @Override
          public void onSubscribe(@NonNull Subscription s) {
              System.out.println(&quot;Flowable onSubs&quot;);
          }
  
          @Override
          public void onNext(Object o) {
              System.out.println(&quot;Flowable onNext&quot;);
          }
  
          @Override
          public void onError(Throwable t) {
              System.out.println(&quot;Flowable onErr&quot;);
          }
  
          @Override
          public void onComplete() {
              System.out.println(&quot;Flowable onComlet&quot;);
          }
      };
  </code></pre>
  <p>Logs are:</p>
  <pre><code>Running...
  Flowable onSubs
  </code></pre>
  <p>If I use lambdas it works, but there is not onSubscribe callback.</p>
  <p>How can I get a subscription and why these mathods haven't been called?</p>