title: Why can't I use the null-coalescing operator like this?
body: <p>According to <a href="http://msdn.microsoft.com/en-us/library/ms173224.aspx" rel="nofollow">MSDN</a>:</p>
  
  <blockquote>
    <p>The ?? operator is called the null-coalescing operator and is used to
    define a default value for nullable value types or reference types.</p>
  </blockquote>
  
  <p>But when I run the code below:</p>
  
  <pre><code>Guid test;
  Guid otherGuid = test ?? Guid.NewGuid();
  </code></pre>
  
  <p>I get the error:</p>
  
  <blockquote>
    <p>Operator '??' cannot be applied to operands of type 'System.Guid' and
    'System.Guid'</p>
  </blockquote>
  
  <p>I thought Guid was a reference type. Is that not the case?  Could someone explain to my why this does not work?</p>