title: Scheme: how to check if void
body: <p>I get this error :</p>
  
  <pre><code>cdr: expects argument of type &lt;pair&gt;; given #&lt;void&gt;
  </code></pre>
  
  <p>and checking if <code>(null? argument)</code> isn't working<br>
  I searched alot for <code>void?</code> function , but I could find anything 
  so , any ideas ppl :)<br>
  thanks a million in advance</p>