title: Regex - Not null parameter
body: <p>I use this expression to check if the paramater <strong>is null or not null</strong>:</p>
  
  <pre><code>^$
  </code></pre>
  
  <p>But it does the opposite that I want. </p>
  
  <p>How can I check if it is <strong>not null</strong>?</p>