public static Stream<Path> walkFileSystem(FileSystem fileSystem) {
    return StreamSupport.stream(fileSystem.getRootDirectories().spliterator(), false)
      .flatMap(rootDirectory -> {
        try {
          return Files.walk(rootDirectory, FileVisitOption.FOLLOW_LINKS);
        } catch (IOException e) {
          LOGGER.error("Unable to walk " + rootDirectory + " in " + fileSystem, e);
          return Stream.empty();
        }
      });
  }
Returns a stream that lists all files in {@code fileSystem}.
planetiler-core/src/main/java/com/onthegomap/planetiler/util/FileUtils.java