docs: def render_unregistered(error=None):
      """
      Render template file for the unregistered user.
  
      Args:
          error (str, default None): Optional error message.
  
      Returns:
          str: Template filled with data.
      """
      return template(
          read_index_template(),
          registered=False,
          error=error,
          seeder_data=None,
          url_id=None,
      )