title: jsr 303 validate a number and auto initialize to 0
body: <p>in my domain class I have an integer which is being populated from
  form. if user enters any digit , it will be validated and if he leaves
  the input box empty, it will default initialize to 0</p>
  
  <p>so far I have done the first part with </p>
  
  <pre><code>@NumberFormat(style = Style.NUMBER)
  </code></pre>
  
  <p>How to go about default initilizing it to 0?</p>