TypeError: Cannot read 'use_v2_feature_versioning' of undefined in feature-list-store

[talissoncosta]

Bug Description

Users encounter a TypeError when editing/toggling features that prevents the operation from completing.

Error: TypeError: Cannot read properties of undefined (reading 'use_v2_feature_versioning')

Sentry Issue: https://flagsmith.sentry.io/issues/7188659117/

Impact

• 5 events / 5 users in 1 day
• First seen: 2026-01-14
• Blocks feature editing operations

Steps to Reproduce

1. Open Flagsmith in multiple browser tabs with different projects
2. Navigate between projects in different tabs
3. On the Features page, click the toggle switch on any feature
4. Click "Confirm" in the toggle confirmation modal
5. Error occurs because ProjectStore has cached environments from a different project

Alternative scenario:

1. Have a browser tab open on the Features page
2. Let the session remain idle for an extended period
3. Try to toggle a feature
4. ProjectStore may be stale or out of sync

Root Cause

In frontend/common/stores/feature-list-store.ts lines 276-278:

const env = ProjectStore.getEnvironment(environmentId)

if (env.use_v2_feature_versioning) {  // env can be undefined

ProjectStore.getEnvironment() returns undefined when the environment isn't found in the cached environments list.

Suggested Fix

Add null check:

const env = ProjectStore.getEnvironment(environmentId)

if (!env) {
  console.error(`Environment ${environmentId} not found in ProjectStore`)
  store.goneABitWest()
  return
}

if (env.use_v2_feature_versioning) {

Files to Modify

• frontend/common/stores/feature-list-store.ts (lines 276-278)
• Same pattern may exist in editFeatureStateChangeRequest function

[talissoncosta]

Additional Affected Code

Found another related Sentry issue with the same root cause:

Sentry Issue: https://flagsmith.sentry.io/issues/7193272016/

Error: TypeError: undefined is not an object (evaluating '_.find(p.environments,{api_key:this.props.environmentId}).name')

This is the same pattern - _.find() returns undefined when the environment isn't found, then accessing .name throws.

Additional files to fix:

frontend/web/components/modals/CreateFlag.js (3 locations):

• Line 1232-1234
• Line 1266-1268
• Line 2177-2179

frontend/web/components/modals/CreateWebhook.js:

• Line 127-129

Suggested fix pattern:

// Before (unsafe)
_.find(project.environments, { api_key: this.props.environmentId }).name

// After (safe)
_.find(project.environments, { api_key: this.props.environmentId })?.name ?? ''

Note: Some files already use the safe pattern (e.g., ConfirmToggleFeature.tsx, CreateTrait.tsx), so this is about consistency across the codebase.

[sentry]

Sentry Issue: FLAGSMITH-FRONTEND-4G7

[sentry]

Sentry Issue: FLAGSMITH-FRONTEND-4G0

[talissoncosta]

Additional Related Sentry Issues

Found more Sentry issues with the same root cause - ProjectStore.model or project.environments being null/stale when accessed:

1. store.model.environments is null

Sentry: https://flagsmith.sentry.io/issues/FLAGSMITH-FRONTEND-49G (screenshot shared)
Error: TypeError: Cannot read properties of null (reading 'environments')
Location: project-store.js:216 in getEnvironmentIdFromKey
Impact: 21 events / 21 users (started Jan 7)

// project-store.js line 215-217
getEnvironmentIdFromKey: (api_key) => {
  const env = _.find(store.model.environments, { api_key })  // store.model can be null!
  return env && env.id
},

2. Undefined .name access

Sentry: https://flagsmith.sentry.io/issues/7173149393/
Error: TypeError: Cannot read properties of undefined (reading 'name')
Impact: 2 events / 2 users
Context: User had two different projects in play (API calls to project 16006 while UI showing project 16491) - classic stale store issue.

---

Summary of All Affected Code

All these issues stem from the same pattern - accessing properties without null checks when ProjectStore data is stale or out of sync:

File	Line(s)	Issue
feature-list-store.ts	276-278	env.use_v2_feature_versioning
project-store.js	216	store.model.environments
CreateFlag.js	1232-1234, 1266-1268, 2177-2179	_.find(...).name
CreateWebhook.js	127-129	_.find(...).name

Suggested Comprehensive Fix

1. Add null checks to all ProjectStore getter methods:

getEnvironmentIdFromKey: (api_key) => {
  if (!store.model?.environments) return null
  const env = _.find(store.model.environments, { api_key })
  return env?.id
},

2. Add null checks before accessing .name on find results:

// Use optional chaining
_.find(project.environments, { api_key: environmentId })?.name ?? ''

3. Consider adding a guard in components that use ProjectStore to ensure data is loaded before rendering.

[sentry]

Sentry Issue: FLAGSMITH-FRONTEND-4FF