Getting Assertion Error from undici library after update to next 15.4.5

[Ortieez]

Summary

Hi, I am getting an error "AssertionError [ERR_ASSERTION]: false == true" after an update to nextjs version 15.4.5, but then when I went a commit back (before update), the error keeps appearing.

It happens only on the /api routes, nothing else affected. First of all it happened only in one /api route but then i moved to different page when I already got the error and the other /api also got the error.

I have:

• redownloaded the project (multiple times)
• reinstalled node_modules (multiple times)
• reinstalled nodejs (used version 18, 22, 24)

I'm hopeless, about this. Spent whole day on trying to fix it.

Additional information

Error track:

  ✓ Compiled /api/improve-description in 493ms
  ⨯ AssertionError [ERR_ASSERTION]: false == true
     at extractBody (node:internal/deps/undici/undici:5986:7)
     at new Request (node:internal/deps/undici/undici:10387:48)
     at new NextRequest (C:\Users\alipe\Documents\vachasoftware\keramika-za-kostelem\.next\server\chunks\node_modules_next_354edd56._.js:5035:14)
     at NextRequestAdapter.fromNodeNextRequest (C:\Users\alipe\Documents\vachasoftware\keramika-za-kostelem\.next\server\chunks\node_modules_next_354edd56._.js:5197:16)
     at handler (C:\Users\alipe\Documents\vachasoftware\keramika-za-kostelem\.next\server\chunks\node_modules_next_451c573d._.js:14299:246)
     at async doRender (C:\Users\alipe\Documents\vachasoftware\keramika-za-kostelem\node_modules\next\dist\server\base-server.js:1587:34)
     at async DevServer.renderToResponseWithComponentsImpl (C:\Users\alipe\Documents\vachasoftware\keramika-za-kostelem\node_modules\next\dist\server\base-server.js:1929:13)
     at async DevServer.renderPageComponent (C:\Users\alipe\Documents\vachasoftware\keramika-za-kostelem\node_modules\next\dist\server\base-server.js:2395:24)
     at async DevServer.renderToResponseImpl (C:\Users\alipe\Documents\vachasoftware\keramika-za-kostelem\node_modules\next\dist\server\base-server.js:2435:32)
     at async DevServer.pipeImpl (C:\Users\alipe\Documents\vachasoftware\keramika-za-kostelem\node_modules\next\dist\server\base-server.js:1035:25)
     at async NextNodeServer.handleCatchallRenderRequest (C:\Users\alipe\Documents\vachasoftware\keramika-za-kostelem\node_modules\next\dist\server\next-server.js:393:17)
     at async DevServer.handleRequestImpl (C:\Users\alipe\Documents\vachasoftware\keramika-za-kostelem\node_modules\next\dist\server\base-server.js:925:17)
     at async C:\Users\alipe\Documents\vachasoftware\keramika-za-kostelem\node_modules\next\dist\server\dev\next-dev-server.js:398:20
     at async Span.traceAsyncFn (C:\Users\alipe\Documents\vachasoftware\keramika-za-kostelem\node_modules\next\dist\trace\trace.js:157:20)
     at async DevServer.handleRequest (C:\Users\alipe\Documents\vachasoftware\keramika-za-kostelem\node_modules\next\dist\server\dev\next-dev-server.js:394:24)
     at async invokeRender (C:\Users\alipe\Documents\vachasoftware\keramika-za-kostelem\node_modules\next\dist\server\lib\router-server.js:239:21)
     at async handleRequest (C:\Users\alipe\Documents\vachasoftware\keramika-za-kostelem\node_modules\next\dist\server\lib\router-server.js:436:24)
     at async requestHandlerImpl (C:\Users\alipe\Documents\vachasoftware\keramika-za-kostelem\node_modules\next\dist\server\lib\router-server.js:464:13)
     at async Server.requestListener (C:\Users\alipe\Documents\vachasoftware\keramika-za-kostelem\node_modules\next\dist\server\lib\start-server.js:218:13) {
   generatedMessage: true,
   code: 'ERR_ASSERTION',
   actual: false,
   expected: true,
   operator: '==',
   page: '/api/improve-description'
}

---
next info:

Operating System:
  Platform: win32
  Arch: x64
  Version: Windows 11 Pro
  Available memory (MB): 32680
  Available CPU cores: 16
Binaries:
  Node: 24.4.0
  npm: 11.5.1
  Yarn: 1.22.21
  pnpm: 9.3.0
Relevant Packages:
  next: 15.4.5 // Latest available version is detected (15.4.5).
  eslint-config-next: 15.4.5
  react: 19.1.1
  react-dom: 19.1.1
  typescript: 5.9.2
Next.js Config:
  output: N/A

---

Dependencies (if useful)

"dependencies": {
        "@ai-sdk/openai": "^2.0.0",
        "@ai-sdk/react": "^2.0.0",
        "@headlessui/react": "^2.2.7",
        "@hello-pangea/dnd": "^18.0.1",
        "@heroicons/react": "^2.2.0",
        "@hookform/error-message": "^2.0.1",
        "@hookform/resolvers": "^5.2.1",
        "@prisma/client": "^6.13.0",
        "@radix-ui/react-alert-dialog": "^1.1.14",
        "@radix-ui/react-dialog": "^1.1.14",
        "@radix-ui/react-icons": "^1.3.2",
        "@radix-ui/react-label": "^2.1.7",
        "@radix-ui/react-select": "^2.2.5",
        "@radix-ui/react-slot": "^1.2.3",
        "@radix-ui/react-tabs": "^1.1.12",
        "@radix-ui/react-toast": "^1.2.14",
        "@radix-ui/react-toggle": "^1.1.9",
        "@radix-ui/react-toggle-group": "^1.1.10",
        "@react-email/components": "0.4.0",
        "@react-email/render": "1.1.4",
        "@react-pdf/renderer": "^4.3.0",
        "@stripe/stripe-js": "^7.7.0",
        "@t3-oss/env-nextjs": "0.13.8",
        "@tailwindcss/aspect-ratio": "^0.4.2",
        "@tailwindcss/forms": "^0.5.10",
        "@tailwindcss/typography": "^0.5.16",
        "@tanstack/react-table": "^8.21.3",
        "@tiptap/react": "^3.0.7",
        "@tiptap/starter-kit": "^3.0.7",
        "@vercel/analytics": "^1.5.0",
        "@vercel/blob": "1.1.1",
        "ai": "^5.0.0",
        "axios": "^1.11.0",
        "babel-plugin-react-compiler": "^19.1.0-rc.2",
        "better-auth": "^1.3.4",
        "class-variance-authority": "^0.7.1",
        "clsx": "^2.1.1",
        "embla-carousel-react": "^8.6.0",
        "heic-to": "^1.2.1",
        "lucide-react": "0.535.0",
        "next": "^15.4.5",
        "next-safe-action": "8.0.8",
        "qrcode": "^1.5.4",
        "react": "19.1.1",
        "react-dom": "19.1.1",
        "react-hook-form": "^7.61.1",
        "react-mobile-cropper": "^0.10.0",
        "resend": "^4.7.0",
        "sharp": "0.34.3",
        "short-unique-id": "^5.3.2",
        "slug": "11.0.0",
        "stripe": "^18.4.0",
        "tailwind-merge": "^3.3.1",
        "ts-node": "^10.9.2",
        "uuid": "^11.1.0",
        "web-streams-polyfill": "^4.1.0",
        "xml2js": "^0.6.2",
        "zod": "^4.0.14",
        "zustand": "^5.0.7"
    },
    "devDependencies": {
        "@next/eslint-plugin-next": "^15.4.5",
        "@tailwindcss/postcss": "^4.1.11",
        "@testing-library/dom": "^10.4.1",
        "@testing-library/jest-dom": "^6.6.4",
        "@testing-library/react": "^16.3.0",
        "@types/jest": "30.0.0",
        "@types/node": "24.1.0",
        "@types/qrcode": "^1.5.5",
        "@types/react": "19.1.9",
        "@types/react-dom": "19.1.7",
        "@types/slug": "^5.0.9",
        "@types/uuid": "^10.0.0",
        "@types/xml2js": "^0.4.14",
        "@typescript-eslint/parser": "^8.38.0",
        "concurrently": "^9.2.0",
        "eslint": "^9.32.0",
        "eslint-config-next": "^15.4.5",
        "eslint-plugin-jest-dom": "^5.5.0",
        "framer-motion": "^12.23.12",
        "jest": "^30.0.5",
        "jest-environment-jsdom": "^30.0.5",
        "jest-mock-extended": "^4.0.0",
        "prettier": "^3.6.2",
        "prettier-plugin-tailwindcss": "^0.6.14",
        "prisma": "^6.13.0",
        "tailwindcss": "^4.1.11",
        "ts-jest": "^29.4.0",
        "tw-animate-css": "^1.3.6",
        "typescript": "^5.9.2"
    },

Example

No response

[Ortieez]

Okay problem found, it was with the web-streams-polyfill dependency, needed for proper support for rendering react email templates in page.

[ridays2001]

Thank you! I faced the exact same issue. I removed this dependency and everything started working, lol