title: Field with null or empty string value doesn't show up at all in Kafka topic when published
body: <p>When I publish a payload to a kafka topic, if a particular field has a null value, or empty string, then the field doesn’t show up in the payload at all in the kafka topic.  I want the field to still show, with null or empty string value.</p>
  <p>For example if I publish a payload with 2 fields, one field named <code>firstname</code> and value “<code>Sara</code>”, and also another field named <code>lastname</code> with a value of <code>null</code> or <code>“”</code>,  then in the kafka topic there is only the <code>firstname</code> field with value “<code>Sara</code>”, and there is no <code>lastname</code> field displayed at all.  I want <code>lastname</code> field to display with value of <code>null</code> or <code>“”</code>.</p>
  <p>Can someone please help me understand why this is happening?  I'm viewing the data through Lenses.io so maybe that UI is simply not showing the null values?  Is there possibly some config to set when configuring the KafkaProducer in my java code, or some config on the Kafka cluster that is causing this?</p>