title: Mono.flatMap is not getting invoked
body: <p>I am still new to Spring Webflux and flatMap on Mono doesn't seem to work.
   I have the following function and call to <em>kafkaPublisher.publishToTopic</em> is not working. I inserted the print statement to test if it prints anything and it doesn't even execute the print statement. <em>publishToTopic</em> returns <code>Mono&lt;Void&gt;</code>.    </p>
  
  <pre><code>private Mono&lt;Void&gt; test(Long gId, UUID pId) {
      Mono&lt;UUID&gt; nId = pDao.findNId(pId);
      Mono&lt;List&lt;String&gt;&gt; channels = nId.flatMapMany(pDao::findChannels).collectList();
      return Mono.zip(nId, channels)
             .flatMap(t -&gt; {
                 System.out.println(t.getT1());
                 return kafkaPublisher.publishToTopic(gId, t.getT1().toString(), t.getT2());
             });
  </code></pre>
  
  <p>}</p>
  
  <p>It gets invoked if <code>.block</code> is called on <code>flatMap</code> as shown below.</p>
  
  <pre><code>private Mono&lt;Void&gt; test(Long gId, UUID pId) {
      Mono&lt;UUID&gt; nId = pDao.findNId(pId);
      Mono&lt;List&lt;String&gt;&gt; channels = nId.flatMapMany(pDao::findChannels).collectList();
      Mono.zip(nId, channels)
             .flatMap(t -&gt; {
                 System.out.println(t.getT1());
                 return kafkaPublisher.publishToTopic(gId, t.getT1().toString(), t.getT2());
             }).block();
      return Mono.empty();
  </code></pre>
  
  <p>}</p>