title: Remove array field if empty
body: <p>Please suggest how to remove array field if empty? I have tried below config :</p>
  
  <pre><code>if [tags] == [] {
  mutate {
  remove_field =&gt; ["tags"]
  }
  }
  
  But getting logstash exception:
  [2018-03-01T15:07:56,000][FATAL][logstash.runner ] The given configuration is invalid. Reason: Failed to parse right-hand side of conditional [str]pipeline:31:8:[tags] == []
  </code></pre>