ESM importing all files from folder with index.js not working

Consider this very simple project: esm-test

Runs on NodeJS 13.

This project has "type":"module" in his package.json so Node will treat by default all files .js as ECMAScript Modules. See: ECMAScript Modules - Enabling.

It has the following very simple structure:

- package.json
- src/
  - stuff/
    - a.js
    - b.js
    - index.js
  - app.js

The file app.js is the package entry point.

My purpose is to import all files from stuff/ folder using the index.js file. I know that in ES6, having an index.js file in a folder lets you perform an import from the folder implicitly without specifying the index.js in the import statement.

So I can do:

import { a, b } from './stuff'

Instead of:

import a from './stuff/a.js'
import b from './stuff/b.js'

But it's not working for me. It shows the following error:

internal/modules/esm/default_resolve.js:96
  let url = moduleWrapResolve(specifier, parentURL);
            ^

Error: Cannot find module C:\projects\esm-test\src\stuff imported from C:\projects\esm-test\src\app.js
    at Loader.resolve [as _resolve] (internal/modules/esm/default_resolve.js:96:13)
    at Loader.resolve (internal/modules/esm/loader.js:72:33)
    at Loader.getModuleJob (internal/modules/esm/loader.js:156:40)
    at ModuleWrap.<anonymous> (internal/modules/esm/module_job.js:42:40)
    at link (internal/modules/esm/module_job.js:41:36) {
  code: 'ERR_MODULE_NOT_FOUND'
}

Can you help me with this please.