code: public FolderItemsResponse listItems(String accountId, String folderId) throws ApiException {
      return listItems(accountId, folderId, null);
    }
docs: Gets a list of the envelopes in the specified folder.
  Retrieves a list of the envelopes in the specified folder. You can narrow the query by specifying search criteria in the query string parameters.
  @param accountId The external account number (int) or account ID Guid. (required)
  @param folderId The ID of the folder being accessed. (required)
  @return FolderItemsResponse