title: In logs I see KafkaTopicPartition cannot be used as a POJO; what does that mean?
body: <p>Not an error but I do see this line that according to the message might effect performance: </p>
  
  <pre><code>2019-01-02 14:44:44,879 INFO  org.apache.flink.api.java.typeutils.TypeExtractor             
  - class org.apache.flink.streaming.connectors.kafka.internals.KafkaTopicPartition 
  does not contain a setter for field topic
  2019-01-02 14:44:44,879 INFO  org.apache.flink.api.java.typeutils.TypeExtractor             
  - Class class org.apache.flink.streaming.connectors.kafka.internals.KafkaTopicPartition 
  cannot be used as a POJO type because not all fields are valid POJO fields, 
  and must be processed as GenericType. Please read the Flink documentation on "Data Types &amp; Serialization" 
  for details of the effect on performance.
   2019-01-02 14:44:44,884 INFO  org.apache.flink.streaming.connectors.kafka.FlinkKafkaConsumerBase  - No restore state for FlinkKafkaConsumer.
  </code></pre>
  
  <p>Is this something that I can/need to do about it ?</p>