public ImmutableList<Path> walk() throws IOException {
    try (Stream<Path> fileStream = Files.walk(rootDir)) {
      return fileStream.filter(pathFilter).sorted().collect(ImmutableList.toImmutableList());
    }
  }
Walks {@link #rootDir}.

@return the walked files.
@throws IOException if walking the files fails.
jib-core/src/main/java/com/google/cloud/tools/jib/filesystem/DirectoryWalker.java