URL search parameters including spaces are duplicated after middleware rewrite

### Link to the code that reproduces this issue https://github.com/federicobadini/search-param-bug-repro ### To Reproduce When using Next.js middleware to perform a rewrite, URL search parameters containing spaces (encoded as +) result in duplicated query parameters—one with the expected value, and one with an empty string. To replicate the bug simply: - run the minimal reproduction - check the default behaviour by clicking on the `Trigger buggy behaviour` button - check the workaround via `Trigger fixed behaviour` If you prefer, the minimal repro is already deployed on Vercel here: https://search-param-bug-repro.vercel.app/ ### Current vs. Expected behavior When a request with a query string containing + (e.g., ?q=hello+world) hits a middleware that rewrites the path, the resulting request seems to reach the page with two parameters instead of just one: q=hello world ✅ (decoded correctly) q="" ❌ (duplicate with empty value) ### Provide environment information ```bash Operating System: Platform: darwin Arch: arm64 Version: Darwin Kernel Version 24.4.0: Fri Apr 11 18:33:47 PDT 2025; root:xnu-11417.101.15~117/RELEASE_ARM64_T6000 Available memory (MB): 32768 Available CPU cores: 10 Binaries: Node: 20.18.2 npm: 10.8.2 Yarn: 1.22.19 pnpm: N/A Relevant Packages: next: 15.2.3 // There is a newer version (15.3.2) available, upgrade recommended! eslint-config-next: 15.3.2 react: 19.1.0 react-dom: 19.1.0 typescript: 5.8.3 Next.js Config: output: N/A ``` ### Which area(s) are affected? (Select all that apply) Middleware ### Which stage(s) are affected? (Select all that apply) Vercel (Deployed) ### Additional context The suggested workaround - manually re-encoding the search parameters using encodeURIComponent() before the middleware rewrite - was discovered after extensive debugging. This approach appears to prevent the issue entirely. It seems likely that Next.js performs some internal handling of the query string during the rewrite process, and …