Failed To Compile - npm run build after upgrading Next JS

Bug report

Describe the bug

I upgraded next 5.1.0 to next 8.1.0 using this command npm i --save next@latest react@latest react-dom@latest when I’m running npm run build command, this error occurs

λ npm run build

> inviteman@0.0.1 build D:\Documents\GitHub\inviteman
> next build src && npm run build:server

Creating an optimized production build ...

Failed to compile.

../node_modules/next-server/dist/lib/head-manager-context.js
Error: .env["debug"] must be an object, or undefined
    at Array.forEach (<anonymous>)

> Build error occurred
Error: > Build failed because of webpack errors
    at Object.build [as default] (D:\Documents\GitHub\inviteman\node_modules\next\dist\build\index.js:192:15)
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! inviteman@0.0.1 build: `next build src && npm run build:server`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the inviteman@0.0.1 build script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     C:\Users\Irene\AppData\Roaming\npm-cache\_logs\2019-04-21T15_52_07_208Z-debug.log

To Reproduce

Steps to reproduce the behavior, please provide code snippets or a repository:

1. Upgrade next JS npm i --save next@latest react@latest react-dom@latest
2. Run npm run build
3. See error

System information

• OS: Windows 10
• Version of Next.js: 8.1.0

[timneutkens]

Please provide a full reproduction.

[lkbr]

Not on the Next team, but usually the most helpful thing is a link to a repository of a stock install of Next.js with the minimal amount of code and npm packages needed to recreate the error.

Quite often, this process of stripping down the code/packages and trying to reproduce the problem will lead you to your own solution or to find that the problem was not with Next but with your own custom code or a third party package.

Having done this, you now either have strong case to show that the issue is with Next, or you know the problem is with a third party package and can approach them, or you have a lot of context to ask for help (https://spectrum.chat/next-js being the preferred place to ask).

The final benefit is that you’ve saved the Next team from having to do this for you, and maybe they can use that saved time to further improve Next for us all.