I am trying to learn how to programmatically set the value in a WebDropDown object (on the client).  Here is my test code:

function SetTo(value) {
  var combo = $find('<%= wddRoles.ClientID %>');
  var items = combo.get_items();
  var index = -1 
  console.log(items);   // returning NULL
  for (var i = 0; i < items.length; i++) {
      var item = items[i];
      if (item.get_element().get_value() == value) {
          index = i;
      }
  }
  console.log(index);
  combo.set_selectedItemIndex(index);

}     

As shown in the comments, the statement combo.get_items(); is returning null. I have checked the combo variable, and it is being set (i.e. it is not null).

Any thoughts on how to set the selectedIndex or selectedItem in a WebDropDown?