fix: add null checks for multivariate_options in feature-list-store

[talissoncosta]

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Changes

Closes #6552

Adds defensive null checks for originalFlag.multivariate_options in the editFeatureMv function to prevent crashes when editing multivariate feature flags with incomplete store data.

Root Cause: When originalFlag exists in the store but multivariate_options is undefined, the code crashes with:

TypeError: Cannot read properties of undefined (reading 'multivariate_options')

Fix:

• Line 222-225: Added originalFlag?.multivariate_options check before accessing .find()
• Line 247: Added fallback to empty array (originalFlag?.multivariate_options || [])

Sentry Issue: FLAGSMITH-FRONTEND-48Y - 47 events, 15 users affected

How to reproduce

1. Navigate to a project's Features page
2. Create or select a feature with multivariate options
3. Open the feature modal to edit it
4. The error occurs when the store has the feature but multivariate_options is undefined (race condition or stale data)

Alternative reproduction (simulating the bug):

1. Open Chrome DevTools → Sources tab
2. Navigate to a feature with multivariate options
3. Set a breakpoint in feature-list-store.ts at the editFeatureMv function
4. Manually set originalFlag.multivariate_options = undefined in the console
5. Continue execution → observe the crash

After the fix: The code gracefully handles undefined multivariate_options by using optional chaining and fallback to empty array.

How did you test this code?

• Verified the fix aligns with the proposed solution in Fix: TypeError when editing multivariate feature flags - missing null check on originalFlag.multivariate_options #6552
• ESLint passed via pre-commit hook
• The changes are defensive null checks that won't affect normal operation when multivariate_options exists

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Project	Deployment	Review	Updated (UTC)
flagsmith-frontend-preview	Ready	Preview, Comment	Jan 20, 2026 4:36pm
flagsmith-frontend-staging	Ready	Preview, Comment	Jan 20, 2026 4:36pm

1 Skipped Deployment

Project	Deployment	Review	Updated (UTC)
docs	Ignored		Jan 20, 2026 4:36pm

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Docker builds report

Image	Build Status	Security report
ghcr.io/flagsmith/flagsmith-api-test:pr-6561	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-e2e:pr-6561	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-api:pr-6561	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith:pr-6561	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-private-cloud:pr-6561	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-frontend:pr-6561	Finished ✅	Results ✅