title: Merge flow files on condition based using nifi?
body: <p>I had a 3 flowfiles which are coming from the same processor.</p>
  
  <p>FF1 -> {a:1,b:2,c:'name'}</p>
  
  <p>FF2 -> {a:1,b:5,c:'fruit'}</p>
  
  <p>FF3 -> {a:2,b:3,c:'abc'}</p>
  
  <p>By using MergeContent Processor I'm able to merge all the flow files, but my requirement is to merge flow files on Key.</p>
  
  <p>Expected output if I join with Key 'a':</p>
  
  <p>FF1 -> [{a:1,b:2,c:'name'},{a:1,b:5,c:'fruit'}]</p>
  
  <p>FF2 -> [{a:2,b:3,c:'abc'}]</p>