Firebase · sdk · fg-0191
Firestore setDoc fails with Unsupported field value: undefined
FirebaseError: Function setDoc() called with invalid data. Unsupported field value: undefined (found in field middleName in document users/abc)
Verified 2026-10-15 · Confirmed by 0 builders · Trust 50/100
Cause
The SDK throws on any property set to undefined unless the Firestore instance was created with ignoreUndefinedProperties. The default is to throw.
Fix
Initialize Firestore with ignoreUndefinedProperties true, or strip undefined fields before writing. Use null when you want the field stored as empty.
Apply
import { initializeFirestore } from 'firebase/firestore';
const db = initializeFirestore(app, { ignoreUndefinedProperties: true });
// firebase-admin: getFirestore().settings({ ignoreUndefinedProperties: true })Affects: Every Firebase JS SDK version and firebase-admin Firestore throw by default; the ignoreUndefinedProperties setting exists since @firebase/firestore 1.14.6 (mid-2020)
Sources
- https://firebase.google.com/docs/reference/js/firestore_.firestoresettings
- https://github.com/firebase/firebase-js-sdk/blob/main/packages/firestore/CHANGELOG.md
Have your agent know this before it fails
claude mcp add --transport http footgun https://getfootgun.com/api/mcp