env vars declared in .env[.(development|production)] are undefined at runtime.

[NotArpit]

Link to the code that reproduces this issue

npx create-next-app

To Reproduce

Inside of a fetch function call in next.jsv14 pass in a URL populated as an environment variable.

  const res = await fetch(
    process.env.API_ENDPOINT,
    {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
      },
      body: JSON.stringify({}),
    },
  )

Current vs. Expected behavior

During runtime - this throws the following error:

 ⨯ ../node_modules/.pnpm/next@14.1.0_@babel+core@7.23.9_react-dom@18.2.0_react@18.2.0/node_modules/next/dist/server/lib/patch-fetch.js (258:81) @ toString
 ⨯ TypeError: Cannot read properties of undefined (reading 'toString')

It seems as though the environment variable is undefined at runtime. This issue does not occur when I replace process.env.API_ENDPOINT with the hard-coded string of API endpoint.

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 23.3.0: Wed Dec 20 21:30:44 PST 2023; root:xnu-10002.81.5~7/RELEASE_ARM64_T6000
Binaries:
  Node: 20.11.1
  npm: 10.2.4
  Yarn: 1.22.21
  pnpm: 8.15.3
Relevant Packages:
  next: 14.1.0
  eslint-config-next: 14.1.0
  react: 18.2.0
  react-dom: 18.2.0
  typescript: 5.3.3
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

Data fetching (gS(S)P, getInitialProps)

Which stage(s) are affected? (Select all that apply)

next dev (local)

Additional context

No response

[github-actions]

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I did not open this issue, but it is relevant to me, what can I do to help?

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Useful Resources

• How to Contribute to Open Source (Next.js)
• How to create a Minimal, Complete, and Verifiable example
• Reporting a Next.js bug
• Next.js Triaging issues