Raises:
    FileExistsError: Iff `output_dir` is not empty and `overwrite` is false.
  """
  dir_not_empty = (
      output_dir is not None
      and file_io.file_exists_v2(output_dir)
      and file_io.list_directory_v2(output_dir)
  )

  if dir_not_empty and not overwrite:
    raise FileExistsError(
        f'Output directory already exists: {output_dir} . '
        'Please set overwrite_output_directory to true to '