code: private void addToJsonArray(String key, JsonValue value){
          if (value == null){
              throw new NullPointerException("Value cannot be null.");
          }
          
          PiwikJsonArray a = (PiwikJsonArray)parameters.get(key);
          if (a == null){
              a = new PiwikJsonArray();
              parameters.put(key, a);
          }
          a.add(value);
      }
docs: Add a value to the json array at the specified parameter
  @param key the key of the json array to add to
  @param value the value to add.  Cannot be null