webpack doesn't find configuration

[daton89]

➜ npm run dev

[email protected] dev /Users/tony/Projects/react-redux-blog node ./node_modules/webpack-dev-server/bin/webpack-dev-server.js

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. -> A non-empty string