title: Logstash - remove deep field from json file
body: <p>I have JSON file that I'm sending to ES through logstash.  I would like to remove 1 field ( It's deep field ) in the JSON - ONLY if the value is NULL.</p>
  
  <p>Part of the JSON is:</p>
  
  <pre><code>"input": {
          "startDate": "2015-05-27",
          "numberOfGuests": 1,
          "fileName": "null",
          "existingSessionId": "XXXXXXXXXXXXX",
          **"radius": "null",**
          "nextItemReference": "51",
          "longitude": -99.12,
          "endDate": "2015-05-29",
          "thumbnailHeight": 200,
          "thumbnailWidth": 300,
          "latitude": 19.42,
          "numOfRooms": "1"
      },
  </code></pre>
  
  <p>Part in the <code>logstash.conf</code> file is :</p>
  
  <pre><code>if [input.radius] == "null" {
                  mutate {
                          remove_field =&gt; [ "input.radius" ]
                  }
          }
  </code></pre>
  
  <p>This is inside the filter of course.</p>
  
  <p>How can I remove this field if the value is null?</p>