title: How to get key & value from Kafka RecordHeaders
body: <p>I have a <code>ProducerRecord</code> object.</p>
  <pre><code>ProducerRecord&lt;String, byte[]&gt; hdr = addHeader.addMDGHeader(record);
  </code></pre>
  <p>I'm trying to write a test that checks a particular header key exists.</p>
  <p>If I print <code>hdr.headers().toString()</code> I get the following <code>RecordHeaders(headers = [RecordHeader(key = mdpHeader, value = [123, 34, 83, 101, 113, 117, 101, 110, 99, 101, 78, 111, 34, 58, 48, 44, 34, 84, 101, 109, 112, 108, 97, 116, 101, 115, 34, 58, 91, 93, 125])], isReadOnly = false)</code>.</p>
  <p>How do I pull out <code>mdpHeader</code>?</p>