FB18279120 - Extensions Settings show "(null)" with http://localhost:8000 Safari web app

[lapcat]

1. Run a local web server, for example using /usr/bin/python3 -m http.server in Terminal.
2. Open http://localhost:8000 in Safari
3. Add to Dock...
4. Open the new Safari web app
5. Open the Settings and select the Extensions pane

"Can read and alter sensitive information in “Localhost”, including passwords, phone numbers, and credit cards, and see your activity on (null)."

See the attached screenshots.