title: C# xml serialization
body: <p>I'm serializing an object to xml in c# and I would like to serialize </p>
  
  <pre><code>public String Marker { get; set; }
  </code></pre>
  
  <p>into</p>
  
  <pre><code>&lt;Marker&gt;&lt;/Marker&gt;
  </code></pre>
  
  <p>when string Marker has no value.</p>
  
  <p>Now I get</p>
  
  <pre><code>&lt;Marker /&gt;
  </code></pre>
  
  <p>for <code>Marker == string.Empty</code> and no Marker node for <code>null</code>.
  How can I get this ?</p>