Bug report

Describe the bug

Pages that start with "api" (eg. api-test) don't generate any CSS (or SASS in my case).

Console output:

[ event ] build page: /api-agreement
[ wait ]  compiling ...
[ ready ] compiled successfully - ready on http://localhost:3000
Could not find files for /api-agreement in .next/build-manifest.json

To Reproduce

• Clone this repo: https://github.com/panta82/nextjs-bug-demo
• npm install
• npm start
• Open: http://localhost:3000/api-test

Expected behavior

You should see red text. Instead, the text is black and there is an error in terminal.

System information

• OS: Ubuntu 19.04
• Browser: Chrome
• Version of Next.js: 9.0.2

Additional context

Related to this probably: #7992
Not fixed all the way, it seems.