[Bug] Converter returns bad value converting `dict[None, Any]`

What are you really trying to do?

I don't know why this would be a thing.

Describe the bug

In test_converter.py,
ok(dict[None, str], {'null': "1"}) passes, but that doesn't really seem like the correct return object.

Minimal Reproduction

Environment/Versions

• OS and processor: [e.g. M1 Mac, x86 Windows, Linux]
• Temporal Version: [e.g. 1.14.0?] and/or SDK version
• Are you using Docker or Kubernetes or building Temporal from source?

Additional context

test_converter.py の失敗しているケース ok(dict[None, str], {'null': "1"}) から始めます。現在の結果を再現し、この型に対する converter の動作を調べます。dict[None, str] に対して期待される戻り値オブジェクトについて合意し、その結果でテストがパスすれば、Issue は完了です。