I am getting the below error when doing next build in my next.js app, after it's been working fine with just next (or npm run dev).

The error:

$ next build

The module 'react-dom' was not found. Next.js requires that you include it in 'dependencies' of your 'package.json'. To add it, run 'npm install --save react-dom'

Creating an optimized production build ...



> Using external babel configuration

> Location: ../.babelrc

Failed to compile.



./pages/_app.js

Module not found: Can't resolve 'next/head' in '../pages'



> Build error occurred

Error: > Build failed because of webpack errors

    at build (.../AppData/Roaming/npm/node_modules/next/dist/build/index.js:7:847)

I started my project by cloning Material UI's next.js example and just use that as it seems updated:

https://github.com/mui-org/material-ui/tree/master/examples/nextjs

However, thinking I just may of have an outdated or broken build, I re-cloned the next.js example and did next build as well, without modifying any files and I get the same error.

How can I fix this?