def var list as char extent no-undo.

11.7

I am geting ERROR:Indeterminate extent is already fixed to a dimension of 4. (13738)

I understand why, but wonder how I can get around the problem... 

DO iNumItems = 1 TO ipData:length:
  oItem = NEW Progress.Json.ObjectModel.JsonObject().
  oItem = ipData:GetJsonObject(iNumItems).

  jsonFields = oItem:GetNames().  <------- this sets the extent....

  DO iFields = 1 TO EXTENT(jsonFields):
    jsonField = jsonFields[iFields].
    CASE oItem:GetType(jsonField):

   : 

   :

END. /*iFields*/

extent(jsonFields) = ?.   <---- do not work....

END. /*iNumFields*/