title: NiFi merge CSV files using MergeRecord
body: <p>i have a stream of JSON records that i convert it into CSV record successfully with <a href="https://stackoverflow.com/questions/50577612/">this</a> instruction. but now i want to merge this CSV records into one CSV file. below is that flow:</p>
  
  <p><a href="https://i.stack.imgur.com/8Lqgi.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/8Lqgi.png" alt="nifi flow"></a></p>
  
  <p>at step 5 i face with around 9K csv record, how do i merge it into one csv file using MergeRecord processor?</p>
  
  <p><strong>my csv header:</strong></p>
  
  <pre><code>field1,field2,field3,field4,field5,field6,field7,field8,field9,field10,field11
  </code></pre>
  
  <p>some of this fields may be null and vary in records.</p>