Uncaught TypeError: s[M].push is not a function

Hi,

I'm creating a little App which is consuming an Odata Service.

In the Detailview I'm trying to create a table showing additional info for the Item you selected in the Mainview beforehand.

When I'm creating the List with a static binding its just working fine. So I tried it using a simple formatter. But when I'm replacing the static address with the formatter its not showing any items. Testing it in Chrome with Developer Tools shows an "s[M].push is not a function" error. Any ideas what that might be?

Formatter function:

count_stock.util.Formatter = {

  sortToBeleg : function (HierId, Node) {

  return"/SortimentSet(HierId='" + HierId + "',Node='" + Node + "')/toBeleg";

  }

detailview.xml

<List

  id="intrynumber"

  mode="{device>/listMode}"

  select="handleListSelect"

  selectionChange="handleListSelect"

  growing="true"

  growingScrollToLoad="true"

  items="{parts:['HierId','Node'], formatter:'count_stock.util.Formatter.sortToBeleg'}">

  <items>

  <ObjectListItem

          .

          .    

          .

</ObjectListItem>

  </items>

  </List>

The formatter shows the correct string when put into a simple textfield. Any ideas?