"Invalid configuration object" after creating a package.json using "npm init"

I had a running webpack configuration. But after using npm init to create the following package.json file:

{


 "name": "y",
  "version": "1.0.0",
  "description": "",
  "main": "app.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "babel-core": "^6.24.0",
    "babel-loader": "^6.4.0",
    "babel-preset-es2015": "^6.24.0",
    "babel-preset-react": "^6.23.0",
    "jshint": "^2.9.4",
    "jshint-loader": "^0.8.4",
    "node-libs-browser": "^2.0.0",
    "webpack": "^2.2.1"
  }
}

and installing the following modules:

npm install babel-core babel-loader jshint jshint-loader node-libs-browser  
babel-preset-es2015 babel-preset-react webpack  --save-dev

I got the error message

Invalid configuration object. Webpack has been initialised using a configuration object that does not match the API schema. - configuration.resolve.extensions[0] should not be empty.

When I tried to restart the dev-server using

webpack-dev-server

What could be the problem?

via user1934212