code: private JsonValue getFromJsonArray(String key, int index){
          PiwikJsonArray a = (PiwikJsonArray)parameters.get(key);
          if (a == null){
              return null;
          }
          
          return a.get(index);
      }
docs: Get the value at the specified index from the json array at the specified
  parameter.
  @param key the key of the json array to access
  @param index the index of the value in the json array
  @return the value at the index in the json array