docs: function convertOut(contact) {
      var value = contact.birthday;
      if (value !== null) {
          // try to make it a Date object if it is not already
          if (!utils.isDate(value)){
              try {
                  value = new Date(value);
              } catch(exception){
                  value = null;
              }
          }
          if (utils.isDate(value)){
              value = value.valueOf(); // convert to milliseconds
          }
          contact.birthday = value;
      }
      return contact;
  }