fix(typescript): guard appendFile against null/undefined for optional multipart file uploads

[devin-ai-integration]

Description

Fixes a regression in TypeScript SDK generation (v3.68.0+) where passing undefined to an optional multipart file upload field crashes with TypeError: Cannot use 'in' operator to search for 'path' in undefined.

The call chain appendFile("file", undefined) → toMultipartDataPart(undefined) → getFileWithMetadata(undefined) → if ("path" in file) blows up because undefined is not an object.

Changes Made

• FormDataWrapper.template.ts: Added if (value == null) { return; } at the top of all 4 appendFile implementations (Node18, Node16, Web, simple). Optional file fields silently skip when null/undefined, restoring pre-3.68.0 tolerance.
• file.ts — getFileWithMetadata(): Added a null guard that throws a clear Error("Cannot upload null or undefined as a file. Ensure the file parameter is provided.") as defense-in-depth if toMultipartDataPart is called directly.
• Unit tests added for both guards (file.test.ts + formDataWrapper.test.template.ts)
• Seed outputs regenerated across all file-upload fixtures

Testing

• Unit tests added/updated
  • file.test.ts: 4 tests covering toBinaryUploadRequest and toMultipartDataPart with null/undefined
  • formDataWrapper.test.template.ts: tests for appendFile silently skipping null/undefined in Node18, Web, and default implementations
• Seed tests: all 8 file-upload fixtures pass
• Local vitest: 415 tests pass in no-custom-config
• CI: 50/50 checks passing

Link to Devin session: https://app.devin.ai/sessions/4b885de21ac744dbb59164c3ba84d68a

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[devin-ai-integration]

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.

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SDK Generation Benchmark Results

Comparing PR branch against median of 5 nightly run(s) on main (latest: 2026-06-25T05:19:47Z).

Full benchmark table (click to expand)

Generator	Spec	main (generator)	main (E2E)	PR (generator)	Delta
ts-sdk	square	236s (n=5)	239s (n=5)	231s	-5s (-2.1%)

main (generator): generator-only time via --skip-scripts (includes Docker image build, container startup, IR parsing, and code generation — this is the same Docker-based flow customers use via fern generate). main (E2E): full customer-observable time including build/test scripts (nightly baseline, informational). Delta is computed against generator-only baseline.
⚠️ = generation exited with a non-zero exit code (timing may not reflect a successful run).
Baseline from nightly runs on main (latest: 2026-06-25T05:19:47Z). Trigger benchmark-baseline to refresh.
Last updated: 2026-06-25 21:19 UTC