title: Print logstash event in ruby filter
body: <p>Hello I'm exporting logs from RabbitMQ. In order to debug, I would like to print the content of the message before applying some regex and base64 decode. I'm trying to do something like this: </p>
  
  <pre><code>input {
    rabbitmq {
          host =&gt; "***host***"
          vhost =&gt; "/"
          exchange =&gt; "Exchange"
          key =&gt; "#"
    }
  }
  
  filter {
    ruby {
          code =&gt; "print event['message']"
    }
  }
  
  output {
    elasticsearch {
          host =&gt; "localhost"
    }
  }
  </code></pre>
  
  <p>But I only have <code>nil</code> values for my messages.</p>