title: Represent null value as empty element in xml jaxb
body: <p>I need to display null value as empty element in jaxb. I am using moxy implementation of jaxb.
  I found this option</p>
  
  <pre><code>@XmlNullPolicy(emptyNodeRepresentsNull = true, nullRepresentationForXml = XmlMarshalNullRepresentation.EMPTY_NODE)
  </code></pre>
  
  <p>Is there any similar extension that can be applied at Class level (for all elements defined in it)</p>