title: request.getHeader("referer") returns NULL - Beginner
body: <p><code>request.getHeader("referer")</code> returns null after I redirect the page. Why it happens? And how can I get the referer ?</p>
  
  <pre><code>redirect(action: "pageUnion", params: [param1: 'something'])
              println("&gt; "+request.getHeader("referer"))
  </code></pre>