title: Specify default value in Hibernate's XML configuration file
body: <p>I'm configuring Hibernate via the mapping configuration file.</p>
  
  <pre><code>&lt;class name="Person" table="person"&gt;
      &lt;id name="id" column="id" type="long"/&gt;
      &lt;property name="name" column="name" type="string"/&gt;
      &lt;property name="age" column="age" type="integer"/&gt;
  &lt;/class&gt;
  </code></pre>
  
  <p>How do I set <code>age</code> to be nullable and default to null?</p>