code: def test_login_url(self, null_auth: bsa.NullAuth) -> None:
      assert null_auth.login_url is None
  
imports: from __future__ import annotations
  import pytest
  from types import ModuleType
  from tornado.web import RequestHandler
  from tests.support.util.api import verify_all
  from tests.support.util.filesystem import with_file_contents, with_file_contents_async
  import bokeh.server.auth_provider
label_desc: Use image node_id 3 for calling the TestNullAuth obj's underlying member method code with example usage: obj.test_login_url(null_auth) without return types