what is "?? "operator in c#?
<blockquote>
  <p><strong>Possible Duplicate:</strong><br>
  <a href="http://stackoverflow.com/questions/827454/what-is-the-operator-for">What is the &ldquo;??&rdquo; operator for?</a>  </p>
</blockquote>



<p>What does the "??" operator perform in an expression ?</p>

<pre><code>   public NameValueCollection Metadata
    {
        get { return metadata ?? (metadata = new NameValueCollection()); }
    }
</code></pre>
