presto-raptor-legacy/src/main/java/io/prestosql/plugin/raptor/legacy/storage/FileStorageService.java/FileStorageService/listFiles
class FileStorageService:    private static List<File> listFiles(File dir, FileFilter filter)
    {
        File[] files = dir.listFiles(filter);
        if (files == null) {
            return ImmutableList.of();
        }
        return ImmutableList.copyOf(files);
    }