title: How to proxy pass when condition (related to param presence) is not met
body: <p>In Nginx I need to proxy pass some of the request made to the homepage.</p>
  <p>Specificaly, I need to proxy pass them in case of URLs like:</p>
  <pre><code>example.com
  example.com/
  example.com/?anyTypeOfParameterButNotP
  </code></pre>
  <p>However, when the request contains <code>?p=</code> parameter in the URL, I would like to handle it the regular way (as if there wasn't any proxy_pass at all).</p>
  <p>So, the URLs I would like not to proxy pass would be:</p>
  <pre><code>example.com/?p=1234
  example.com/?p=1234&amp;foo=bar
  </code></pre>
  <p>How can I achieve that?</p>
  <p>I've tried some if statements, some variables solutions, but I didn't figure out any way to work it out.</p>