title: KafkaConsumer assignment() returns empty
body: <p>I am using</p>
  
  <pre><code>&lt;dependency&gt;
      &lt;groupId&gt;org.apache.kafka&lt;/groupId&gt;
      &lt;artifactId&gt;kafka-clients&lt;/artifactId&gt;
      &lt;version&gt;2.0.1&lt;/version&gt;
  &lt;/dependency&gt;
  </code></pre>
  
  <p>The following piece of codes returns the <strong>non-empty assigned</strong> partitions, but <code>poll(0)</code> deprecated.</p>
  
  <pre><code>val records = kafkaConsumer.poll(0) // &lt;= deprecated
  logInfo(s"Dummy call ${records.count()}")
  
  val partitions = kafkaConsumer.assignment()
  logInfo(s"partitions=${partitions}")
  </code></pre>
  
  <p>The following return <strong>empty</strong> partitions:</p>
  
  <pre><code>val records = kafkaConsumer.poll(Duration.ofMillis(0)) // &lt;= not working
  logInfo(s"Dummy call ${records.count()}")
  
  val partitions = kafkaConsumer.assignment()
  logInfo(s"partitions=${partitions}")
  </code></pre>
  
  <p>Why? Any ideas? Thanks</p>