Can't modify webpack configuration: .default is not a valid Plugin property

[aromot]

Hi,

My conf is: Win7, node v8.12.0, yarn 1.9.2. Here's what I did :

git clone https://github.com/electron-userland/electron-webpack-quick-start.git my-app

I changed package.json, adding:

{

  "electronWebpack": {
    "renderer": {
      "webpackConfig": "webpack.renderer.additions.js"
    }
  }
}

My webpack.renderer.additions.js contains just nothing for the moment (to be sure the problem doesn't come from any third party lib, as you see I plan to use handlebars):

module.exports = {
    module: {
        rules: [
            // {
            //     test: /\.hbs$/,
            //     use: ['handlebars-loader']
            // }
        ]
    }
}

I cleaned the src/renderer/index.js => blank

and when I do yarn dev, I get :

ERROR in ./src/renderer/index.js
Module build failed (from ./node_modules/babel-loader/lib/index.js):
Error: [BABEL] D:\...\my-app\src\renderer\index.js: .default is not a valid Plugin property

How can I fix the problem?
When I remove "electronWebpack..." from package.json, it works fine. It seems I can't modify the webpack conf...