title: Logstash Checking Existence of & Parsing Sub-Field
body: <p>In Logstash I have a JSON payload which I've decoded like so: </p>
  
  <pre><code>filter 
  { 
     json 
     { 
       source =&gt; "payload" 
       target =&gt; "payloadData" 
     }
  }
  </code></pre>
  
  <p>Now I want to check if payloadData._extraData exists, and then deserialise that too. </p>
  
  <p>I've tried this method, working from the example given in <a href="https://stackoverflow.com/questions/30309096/logstash-check-if-field-exists">this related question</a>: </p>
  
  <pre><code>filter 
  { 
     json 
     { 
       source =&gt; "payload" 
       target =&gt; "payloadData" 
     }
     if [payloadData._extraData] =~ /.+/ 
     { 
         sourcce =&gt; "payloadData._extraData"  
         target =&gt; "payloadData.extraData" 
     } 
  }
  </code></pre>
  
  <p>But it doesn't do anything (no crash, no error message, just doesn't do anything) </p>