title: Allow Number object to be null in Tapestry BeanEditor
body: <p>I have an object I'd like to edit via beaneditor. One of the properties is of the <code>Number</code> class.</p>
  
  <p>When I try to display the beaneditor, I get the following error:</p>
  
  <blockquote>
    <p>Parameter 'translate' of component core/PropertyEditBlocks:numberfield
    is bound to null. This parameter is not allowed to be null.</p>
  </blockquote>
  
  <p>When I changed the variable type to <code>Double</code>, everything worked fine.</p>
  
  <p>Does it have anything to do with the fact that <code>Number</code> is an abstract class and cannot be instantiated? In that case, should I provide some sort of a translator or something like that so it uses, <code>Double</code> for example, when editing the value?</p>