Dev-Server returns empty page

- Running Ubuntu 18.04
- Installed yarn according to https://yarnpkg.com/lang/en/docs/install/#debian-stable
git clone https://github.com/blinkenrocket/webedit-react
cd webedit-react
yarn
yarn build
yarn dev
- With google-chrome/firefox accessing http://127.0.0.1:8080/  shows a white page

I can't find any error messages on the dev-webserver window or on the browser console.