title: jaxb marshalling skip empty elements
body: <p>Using JAXB  is it possible to ensure that null values are not marshalled as () empty elements. For instance</p>
  
  <pre><code>public class Contacts {
      @XmlElement(name = "Phone")
      protected List&lt;Phone&gt; phone;
      }
  </code></pre>
  
  <p>currently if one of the phone element is null i get </p>
  
  <pre><code>&lt;contact&gt;
           &lt;/phone&gt;
           &lt;phone&gt;
                  &lt;areacode&gt;919&lt;/areacode&gt;
                  &lt;phonenumber&gt;6785432&lt;/phonenumber&gt;
           &lt;/phone&gt;
      &lt;/contact&gt;
  </code></pre>
  
  <p><strong>i want the following output</strong></p>
  
  <pre><code>&lt;contact&gt;
              &lt;phone&gt;
                     &lt;areacode&gt;919&lt;/areacode&gt;
                     &lt;phonenumber&gt;6785432&lt;/phonenumber&gt;
              &lt;/phone&gt;
     &lt;/contact&gt;
  </code></pre>