docs: def show_periodical_tree_by_issn(issn):
      """
      Render tree using ISSN.
      """
      trees = tree_handler().trees_by_issn(issn)
  
      if not trees:
          abort(404, "Dokument s ISSN '%s' není dostupný." % issn)
  
      return render_trees(
          trees,
          partial(web_tools.compose_tree_path, issn=True)
      )