title: OOP parameter values equal to null
body: <p>I'm just new in learning OOP. I've read many articles so far and tried some tutorials. I just wonder why when declaring parameter on a constructor some values should be nulled.</p>
  
  <pre><code>    function __construct($hostname = NULL, $username = NULL, $password = NULL, $database = NULL)
      {
          $this-&gt;hostname = !empty($hostname) ? $hostname : "";
          $this-&gt;username = !empty($username) ? $username : "";
          $this-&gt;password = !empty($password) ? $password : "";
          $this-&gt;database = !empty($database) ? $database : "";
      }
  </code></pre>
  
  <p>like this. I really want know.</p>