code: public void addExtraInfo(String key, Object value) {
          // Turn extraInfo into map
          Map<String, Object> infoMap = (HashMap<String, Object>)getMapFromJSON(extraInfo);
          // Add value
          infoMap.put(key, value);
  
          // Turn back into string
          extraInfo = getJSONFromMap(infoMap);
      }
docs: Add key value pair to extra info
  
  @param key Key of new item
  @param value New value to add