code: public JSONObject element( String key, Object value ) {
        return element( key, value, new JsonConfig() );
     }
docs: Put a key/value pair in the JSONObject. If the value is null, then the key
  will be removed from the JSONObject if it is present.<br>
  If there is a previous value assigned to the key, it will call accumulate.
  
  @param key A key string.
  @param value An object which is the value. It should be of one of these
  types: Boolean, Double, Integer, JSONArray, JSONObject, Long,
  String, or the JSONNull object.
  @return this.
  @throws JSONException If the value is non-finite number or if the key is
  null.