title: Convert List< Guid > to List< Guid? >
body: <p>What is the best practice to convert List&lt; Guid > to List&lt; Guid? >  </p>
  
  <p>The following does not compile:</p>
  
  <pre><code>public List&lt;Guid?&gt; foo()
  {
      List&lt;Guid&gt; guids = getGuidsList();
      return guids; 
  }
  </code></pre>