class DriveHelper {

    @Nullable
    public Drive.Files.List buildRequest(String query, String fields) throws IOException {
        if (query != null && fields != null) {
            return driveService.generateRequest(query, fields);
        }
        return null;
    }

      DriveHelper(@NonNull GoogleAccountCredential credential,
                @NonNull HttpTransport transport,
                @NonNull JsonFactory jsonFactory);
      DriveHelper(DriveService driveService);

}