React: Cannot set property 'lastEffect' of null

If you update to uglifyjs-webpack-plugin version 2.2.0 the problem is fixed.

This is caused by uglifyjs-webpack-plugin version 2.0.1 in React 16.7.0-alpha as it breaks the new hook feature of React.

You can try using the terser plugin. Here is the link: https://github.com/webpack-contrib/terser-webpack-plugin