title: Set default value of RadDatePicker to NULL when date is not set
body: <p>I'm binding the RadDatePicker to a viewModel dateTime property. when the property is null in database i get 01/01/0001. How to i change this behavior to just leave the date field blank..
  example:</p>
  
  <p>In database     ===>   experiation_date : NULL
  In View(GUI)    ===>   experation_date  : 01/01/0001</p>
  
  <p>Expected Result ===>   experation_date  :  {Blank} </p>