dotenv-expand' "default" expansion not working

[FezVrasta]

Verify canary release

• I verified that the issue exists in Next.js canary release

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 21.3.0: Wed Jan  5 21:37:58 PST 2022; root:xnu-8019.80.24~20/RELEASE_ARM64_T6000
Binaries:
  Node: 16.14.0
  npm: 8.3.1
  Yarn: 3.2.0
  pnpm: N/A
Relevant packages:
  next: 12.1.0
  react: 17.0.2
  react-dom: 17.0.2

warn - Latest canary version not detected, detected: "12.1.0", newest: "12.1.1-canary.1".
Please try the latest canary version (npm install next@canary) to confirm the issue still exists before creating a new issue.
Read more - https://nextjs.org/docs/messages/opening-an-issue

What browser are you using? (if relevant)

No response

How are you deploying your application? (if relevant)

No response

Describe the Bug

If I add a fallback/default value to one of my dotenv variable expansions the operation doesn't succeed.

NEXT_PUBLIC_TEST=${KEY:-default}

Results in:

> console.log(process.env.NEXT_PUBLIC_TEST);
< ":-default}"

Expected Behavior

> console.log(process.env.NEXT_PUBLIC_TEST);
< "default"

This is explained in the dotenv-expand documentation here:
https://github.com/motdotla/dotenv-expand#what-rules-does-the-expansion-engine-follow

To Reproduce

Add the above config to .env and run yarn build.

I noticed that the compiled source of @next/env is missing several parts of the dotenv-expand package (that is for some reason bundled in rather than referenced as external)