docs: def template_error_handler(exception):
      """
      Template error handler
      Renders a template for the error code if exception is know by werkzeug.
      Will attempt to load a template from userland app templates and then
      fall back to boiler templates if not found.
      :param exception: Exception
      :return:
      """
      http_exception = isinstance(exception, exceptions.HTTPException)
      code = exception.code if http_exception else 500
  
      # log exceptions only (app debug should be off)
      if code == 500:
          current_app.logger.error(exception)
  
      template = 'errors/{}.j2'.format(code)
      return render_template(template, error=exception), code