code: public String toJsonString() {
          try {
              JSONArray array = new JSONArray();
              for (PebbleTuple t : tuples.values()) {
                  array.put(serializeTuple(t));
              }
              return array.toString();
          } catch (JSONException je) {
              je.printStackTrace();
          }
          return null;
      }
docs: Returns a JSON representation of this dictionary.
  
  @return a JSON representation of this dictionary