[FOWEPJF255]

Fixes #2048

Reason for this change

When exactly one feature flag is unconfigured, modifyValues takes the manual single-flag branch even though --value was not provided. It interprets undefined as false, so cdk.json receives false after the preview displayed the recommended value true.

Description of changes

Use the manual single-flag branch only when params.value is defined. This keeps the write behavior aligned with buildUpdateObject and preserves explicit single-flag values. Add a regression test for one unconfigured flag whose recommended value is true.

No dependency or IAM permission changes are included.

Validation

• Red/green regression: before the fix, the preview showed true while cdk.json received false; after the fix, the test passes.
• corepack yarn@4.17.1 jest --config jest.config.json --runInBand test/commands/flag-operations.test.ts --coverage=false — 59 tests passed.
• corepack yarn@4.17.1 nx run aws-cdk:compile — passed for aws-cdk and its 9 compile dependencies.
• ESLint on both changed files passed in the repository's eslintrc compatibility mode.
• git diff --check and strict UTF-8 validation passed.

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[maintainer-for-aws]

Automated review

A maintainer will still review this — treat the notes below as a starting point.

📌 Commit 837f667

This PR fixes a one-line logic bug in the experimental cdk flags command: when exactly one unconfigured boolean feature flag remained, cdk flags --set --unconfigured --recommended previewed the correct recommended value but wrote the wrong one to cdk.json. The fix adds params.value !== undefined to the single-flag guard in FlagOperations.modifyValues, so the manual --value branch only applies when a value was explicitly supplied; the --unconfigured single-flag case now falls through to the branch that writes flag.recommendedValue, matching the preview logic in the sibling buildUpdateObject. A targeted regression test reproduces the original scenario and asserts the correct persisted value. The change is minimal, well-scoped, and confirmed against the source. No issues found on this change.

🔴 0 blocking · 🟡 0 recommended · ⚪ 0 optional

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