title: Can we write nested if else condition for performing the operation over the content of CSV files in ApacheNifi?
body: <p>Can we write generic Expression language for the below code snippet in Nifi using processors?
  Let's say I have 2 csv files.
  One csv file has columns: X, Y1, Y2, Z
  Other csv file has columns: X, Y3, Y4, Z
  Output file should have columns: X, Y, Z</p>
  
  <p>where Y= Y1+Y2 in first case.
  Y = Y3+Y4 in second case.</p>
  
  <p>How do we check in Nifi for if else condition, as in if y1, y2 are present then concatenate and form Y. If Y3, Y4 are present then concatenate and form Y.</p>
  
  <p>The code snippet for it looks something like this to populate values of column Y -</p>
  
  <pre><code>If (Y == empty) 
  {
          If (Y1 != empty and Y2 != empty) 
          {
                  Y = concat(Y1, Y2)
          }
          else if (Y4 != empty and Y5 != empty)
          {
                  Y = concat(Y4, Y5)
          }
  }
  </code></pre>