Fork of codesandbox doesn't compile

[megantaylor]

What you were expecting:
Fork https://codesandbox.io/s/github/marmelab/react-admin/tree/master/examples/simple, make changes, code should compile.

What happened instead:
Code fails to compile with this error:

ERROR in ./src/polyfills.ts
Module not found: Error: Can't resolve 'proxy-polyfill/proxy.min.js' in '/sandbox/src'
 @ ./src/polyfills.ts 5:0-38
 @ multi (webpack)-dev-server/client?http://127.0.0.1:8080 (webpack)/hot/dev-server.js ./src/polyfills.ts

Steps to reproduce:
Fork https://codesandbox.io/s/github/marmelab/react-admin/tree/master/examples/simple
open any js file and add console.log("test")
see compile error in terminal

Related code:

https://codesandbox.io/s/elegant-dust-pdqkl?file=/src/comments/CommentEdit.tsx

This is preventing me from creating a simple example of my issue in #6751