code: public StatusCode addItem(String sessionId, String listId, int mediaId) throws MovieDbException {
          return modifyMovieList(sessionId, listId, mediaId, MethodSub.ADD_ITEM);
      }
docs: This method lets users add new items to a list that they created.
  
  A valid session id is required.
  
  @param sessionId
  @param listId
  @param mediaId
  @return
  @throws MovieDbException