diff --git a/.changeset/clean-cameras-check.md b/.changeset/clean-cameras-check.md
new file mode 100644
index 00000000000..572ce9b3e3d
--- /dev/null
+++ b/.changeset/clean-cameras-check.md
@@ -0,0 +1,5 @@
+---
+'@firebase/firestore': minor
+---
+
+Fixed a bug where `UpdateData` did not recognize union types or optional, dot-separated string fields.
diff --git a/common/api-review/firestore-lite.api.md b/common/api-review/firestore-lite.api.md
index 70f9a27dba6..83eebeb488d 100644
--- a/common/api-review/firestore-lite.api.md
+++ b/common/api-review/firestore-lite.api.md
@@ -32,6 +32,9 @@ export class Bytes {
     toUint8Array(): Uint8Array;
 }
 
+// @public
+export type ChildUpdateFields<K extends string, V> = V extends Record<string, unknown> ? AddPrefixToKeys<K, UpdateData<V>> : never;
+
 // @public
 export function collection(firestore: Firestore, path: string, ...pathSegments: string[]): CollectionReference<DocumentData>;
 
@@ -191,7 +194,7 @@ export { LogLevel }
 
 // @public
 export type NestedUpdateFields<T extends Record<string, unknown>> = UnionToIntersection<{
-    [K in keyof T & string]: T[K] extends Record<string, unknown> ? AddPrefixToKeys<K, UpdateData<T[K]>> : never;
+    [K in keyof T & string]: ChildUpdateFields<K, T[K]>;
 }[keyof T & string]>;
 
 // @public
@@ -332,7 +335,7 @@ export class Transaction {
 export type UnionToIntersection<U> = (U extends unknown ? (k: U) => void : never) extends (k: infer I) => void ? I : never;
 
 // @public
-export type UpdateData<T> = T extends Primitive ? T : T extends Map<infer K, infer V> ? Map<UpdateData<K>, UpdateData<V>> : T extends {} ? {
+export type UpdateData<T> = T extends Primitive ? T : T extends {} ? {
     [K in keyof T]?: UpdateData<T[K]> | FieldValue;
 } & NestedUpdateFields<T> : Partial<T>;
 
diff --git a/common/api-review/firestore.api.md b/common/api-review/firestore.api.md
index 56ee1729a4e..2d3fee14117 100644
--- a/common/api-review/firestore.api.md
+++ b/common/api-review/firestore.api.md
@@ -1,522 +1,525 @@
-## API Report File for "@firebase/firestore"
-
-> Do not edit this file. It is a report generated by [API Extractor](https://api-extractor.com/).
-
-```ts
-
-import { EmulatorMockTokenOptions } from '@firebase/util';
-import { FirebaseApp } from '@firebase/app';
-import { LogLevelString as LogLevel } from '@firebase/logger';
-
-// @public
-export function addDoc<T>(reference: CollectionReference<T>, data: WithFieldValue<T>): Promise<DocumentReference<T>>;
-
-// @public
-export type AddPrefixToKeys<Prefix extends string, T extends Record<string, unknown>> = {
-    [K in keyof T & string as `${Prefix}.${K}`]+?: T[K];
-};
-
-// @public
-export function arrayRemove(...elements: unknown[]): FieldValue;
-
-// @public
-export function arrayUnion(...elements: unknown[]): FieldValue;
-
-// @public
-export class Bytes {
-    static fromBase64String(base64: string): Bytes;
-    static fromUint8Array(array: Uint8Array): Bytes;
-    isEqual(other: Bytes): boolean;
-    toBase64(): string;
-    toString(): string;
-    toUint8Array(): Uint8Array;
-}
-
-// @public
-export const CACHE_SIZE_UNLIMITED = -1;
-
-// @public
-export function clearIndexedDbPersistence(firestore: Firestore): Promise<void>;
-
-// @public
-export function collection(firestore: Firestore, path: string, ...pathSegments: string[]): CollectionReference<DocumentData>;
-
-// @public
-export function collection(reference: CollectionReference<unknown>, path: string, ...pathSegments: string[]): CollectionReference<DocumentData>;
-
-// @public
-export function collection(reference: DocumentReference, path: string, ...pathSegments: string[]): CollectionReference<DocumentData>;
-
-// @public
-export function collectionGroup(firestore: Firestore, collectionId: string): Query<DocumentData>;
-
-// @public
-export class CollectionReference<T = DocumentData> extends Query<T> {
-    get id(): string;
-    get parent(): DocumentReference<DocumentData> | null;
-    get path(): string;
-    readonly type = "collection";
-    withConverter<U>(converter: FirestoreDataConverter<U>): CollectionReference<U>;
-    withConverter(converter: null): CollectionReference<DocumentData>;
-}
-
-// @public
-export function connectFirestoreEmulator(firestore: Firestore, host: string, port: number, options?: {
-    mockUserToken?: EmulatorMockTokenOptions | string;
-}): void;
-
-// @public
-export function deleteDoc(reference: DocumentReference<unknown>): Promise<void>;
-
-// @public
-export function deleteField(): FieldValue;
-
-// @public
-export function disableNetwork(firestore: Firestore): Promise<void>;
-
-// @public
-export function doc(firestore: Firestore, path: string, ...pathSegments: string[]): DocumentReference<DocumentData>;
-
-// @public
-export function doc<T>(reference: CollectionReference<T>, path?: string, ...pathSegments: string[]): DocumentReference<T>;
-
-// @public
-export function doc(reference: DocumentReference<unknown>, path: string, ...pathSegments: string[]): DocumentReference<DocumentData>;
-
-// @public
-export interface DocumentChange<T = DocumentData> {
-    readonly doc: QueryDocumentSnapshot<T>;
-    readonly newIndex: number;
-    readonly oldIndex: number;
-    readonly type: DocumentChangeType;
-}
-
-// @public
-export type DocumentChangeType = 'added' | 'removed' | 'modified';
-
-// @public
-export interface DocumentData {
-    [field: string]: any;
-}
-
-// @public
-export function documentId(): FieldPath;
-
-// @public
-export class DocumentReference<T = DocumentData> {
-    readonly converter: FirestoreDataConverter<T> | null;
-    readonly firestore: Firestore;
-    get id(): string;
-    get parent(): CollectionReference<T>;
-    get path(): string;
-    readonly type = "document";
-    withConverter<U>(converter: FirestoreDataConverter<U>): DocumentReference<U>;
-    withConverter(converter: null): DocumentReference<DocumentData>;
-}
-
-// @public
-export class DocumentSnapshot<T = DocumentData> {
-    protected constructor();
-    data(options?: SnapshotOptions): T | undefined;
-    exists(): this is QueryDocumentSnapshot<T>;
-    get(fieldPath: string | FieldPath, options?: SnapshotOptions): any;
-    get id(): string;
-    readonly metadata: SnapshotMetadata;
-    get ref(): DocumentReference<T>;
-}
-
-export { EmulatorMockTokenOptions }
-
-// @public
-export function enableIndexedDbPersistence(firestore: Firestore, persistenceSettings?: PersistenceSettings): Promise<void>;
-
-// @public
-export function enableMultiTabIndexedDbPersistence(firestore: Firestore): Promise<void>;
-
-// @public
-export function enableNetwork(firestore: Firestore): Promise<void>;
-
-// @public
-export function endAt(snapshot: DocumentSnapshot<unknown>): QueryConstraint;
-
-// @public
-export function endAt(...fieldValues: unknown[]): QueryConstraint;
-
-// @public
-export function endBefore(snapshot: DocumentSnapshot<unknown>): QueryConstraint;
-
-// @public
-export function endBefore(...fieldValues: unknown[]): QueryConstraint;
-
-// @public
-export class FieldPath {
-    constructor(...fieldNames: string[]);
-    isEqual(other: FieldPath): boolean;
-}
-
-// @public
-export abstract class FieldValue {
-    abstract isEqual(other: FieldValue): boolean;
-}
-
-// @public
-export class Firestore {
-    get app(): FirebaseApp;
-    toJSON(): object;
-    type: 'firestore-lite' | 'firestore';
-}
-
-// @public
-export interface FirestoreDataConverter<T> {
-    fromFirestore(snapshot: QueryDocumentSnapshot<DocumentData>, options?: SnapshotOptions): T;
-    toFirestore(modelObject: WithFieldValue<T>): DocumentData;
-    toFirestore(modelObject: PartialWithFieldValue<T>, options: SetOptions): DocumentData;
-}
-
-// @public
-export class FirestoreError extends Error {
-    readonly code: FirestoreErrorCode;
-    readonly message: string;
-    readonly name: string;
-    readonly stack?: string;
-}
-
-// @public
-export type FirestoreErrorCode = 'cancelled' | 'unknown' | 'invalid-argument' | 'deadline-exceeded' | 'not-found' | 'already-exists' | 'permission-denied' | 'resource-exhausted' | 'failed-precondition' | 'aborted' | 'out-of-range' | 'unimplemented' | 'internal' | 'unavailable' | 'data-loss' | 'unauthenticated';
-
-// @public
-export interface FirestoreSettings {
-    cacheSizeBytes?: number;
-    experimentalAutoDetectLongPolling?: boolean;
-    experimentalForceLongPolling?: boolean;
-    host?: string;
-    ignoreUndefinedProperties?: boolean;
-    ssl?: boolean;
-}
-
-// @public
-export class GeoPoint {
-    constructor(latitude: number, longitude: number);
-    isEqual(other: GeoPoint): boolean;
-    get latitude(): number;
-    get longitude(): number;
-    toJSON(): {
-        latitude: number;
-        longitude: number;
-    };
-}
-
-// @public
-export function getDoc<T>(reference: DocumentReference<T>): Promise<DocumentSnapshot<T>>;
-
-// @public
-export function getDocFromCache<T>(reference: DocumentReference<T>): Promise<DocumentSnapshot<T>>;
-
-// @public
-export function getDocFromServer<T>(reference: DocumentReference<T>): Promise<DocumentSnapshot<T>>;
-
-// @public
-export function getDocs<T>(query: Query<T>): Promise<QuerySnapshot<T>>;
-
-// @public
-export function getDocsFromCache<T>(query: Query<T>): Promise<QuerySnapshot<T>>;
-
-// @public
-export function getDocsFromServer<T>(query: Query<T>): Promise<QuerySnapshot<T>>;
-
-// @public
-export function getFirestore(app?: FirebaseApp): Firestore;
-
-// @public
-export function increment(n: number): FieldValue;
-
-// @public
-export function initializeFirestore(app: FirebaseApp, settings: FirestoreSettings): Firestore;
-
-// @public
-export function limit(limit: number): QueryConstraint;
-
-// @public
-export function limitToLast(limit: number): QueryConstraint;
-
-// @public
-export function loadBundle(firestore: Firestore, bundleData: ReadableStream<Uint8Array> | ArrayBuffer | string): LoadBundleTask;
-
-// @public
-export class LoadBundleTask implements PromiseLike<LoadBundleTaskProgress> {
-    catch<R>(onRejected: (a: Error) => R | PromiseLike<R>): Promise<R | LoadBundleTaskProgress>;
-    onProgress(next?: (progress: LoadBundleTaskProgress) => unknown, error?: (err: Error) => unknown, complete?: () => void): void;
-    then<T, R>(onFulfilled?: (a: LoadBundleTaskProgress) => T | PromiseLike<T>, onRejected?: (a: Error) => R | PromiseLike<R>): Promise<T | R>;
-}
-
-// @public
-export interface LoadBundleTaskProgress {
-    bytesLoaded: number;
-    documentsLoaded: number;
-    taskState: TaskState;
-    totalBytes: number;
-    totalDocuments: number;
-}
-
-export { LogLevel }
-
-// @public
-export function namedQuery(firestore: Firestore, name: string): Promise<Query | null>;
-
-// @public
-export type NestedUpdateFields<T extends Record<string, unknown>> = UnionToIntersection<{
-    [K in keyof T & string]: T[K] extends Record<string, unknown> ? AddPrefixToKeys<K, UpdateData<T[K]>> : never;
-}[keyof T & string]>;
-
-// @public
-export function onSnapshot<T>(reference: DocumentReference<T>, observer: {
-    next?: (snapshot: DocumentSnapshot<T>) => void;
-    error?: (error: FirestoreError) => void;
-    complete?: () => void;
-}): Unsubscribe;
-
-// @public
-export function onSnapshot<T>(reference: DocumentReference<T>, options: SnapshotListenOptions, observer: {
-    next?: (snapshot: DocumentSnapshot<T>) => void;
-    error?: (error: FirestoreError) => void;
-    complete?: () => void;
-}): Unsubscribe;
-
-// @public
-export function onSnapshot<T>(reference: DocumentReference<T>, onNext: (snapshot: DocumentSnapshot<T>) => void, onError?: (error: FirestoreError) => void, onCompletion?: () => void): Unsubscribe;
-
-// @public
-export function onSnapshot<T>(reference: DocumentReference<T>, options: SnapshotListenOptions, onNext: (snapshot: DocumentSnapshot<T>) => void, onError?: (error: FirestoreError) => void, onCompletion?: () => void): Unsubscribe;
-
-// @public
-export function onSnapshot<T>(query: Query<T>, observer: {
-    next?: (snapshot: QuerySnapshot<T>) => void;
-    error?: (error: FirestoreError) => void;
-    complete?: () => void;
-}): Unsubscribe;
-
-// @public
-export function onSnapshot<T>(query: Query<T>, options: SnapshotListenOptions, observer: {
-    next?: (snapshot: QuerySnapshot<T>) => void;
-    error?: (error: FirestoreError) => void;
-    complete?: () => void;
-}): Unsubscribe;
-
-// @public
-export function onSnapshot<T>(query: Query<T>, onNext: (snapshot: QuerySnapshot<T>) => void, onError?: (error: FirestoreError) => void, onCompletion?: () => void): Unsubscribe;
-
-// @public
-export function onSnapshot<T>(query: Query<T>, options: SnapshotListenOptions, onNext: (snapshot: QuerySnapshot<T>) => void, onError?: (error: FirestoreError) => void, onCompletion?: () => void): Unsubscribe;
-
-// @public
-export function onSnapshotsInSync(firestore: Firestore, observer: {
-    next?: (value: void) => void;
-    error?: (error: FirestoreError) => void;
-    complete?: () => void;
-}): Unsubscribe;
-
-// @public
-export function onSnapshotsInSync(firestore: Firestore, onSync: () => void): Unsubscribe;
-
-// @public
-export function orderBy(fieldPath: string | FieldPath, directionStr?: OrderByDirection): QueryConstraint;
-
-// @public
-export type OrderByDirection = 'desc' | 'asc';
-
-// @public
-export type PartialWithFieldValue<T> = T extends Primitive ? T : T extends {} ? {
-    [K in keyof T]?: PartialWithFieldValue<T[K]> | FieldValue;
-} : Partial<T>;
-
-// @public
-export interface PersistenceSettings {
-    forceOwnership?: boolean;
-}
-
-// @public
-export type Primitive = string | number | boolean | undefined | null;
-
-// @public
-export class Query<T = DocumentData> {
-    protected constructor();
-    readonly converter: FirestoreDataConverter<T> | null;
-    readonly firestore: Firestore;
-    readonly type: 'query' | 'collection';
-    withConverter(converter: null): Query<DocumentData>;
-    withConverter<U>(converter: FirestoreDataConverter<U>): Query<U>;
-}
-
-// @public
-export function query<T>(query: Query<T>, ...queryConstraints: QueryConstraint[]): Query<T>;
-
-// @public
-export abstract class QueryConstraint {
-    abstract readonly type: QueryConstraintType;
-}
-
-// @public
-export type QueryConstraintType = 'where' | 'orderBy' | 'limit' | 'limitToLast' | 'startAt' | 'startAfter' | 'endAt' | 'endBefore';
-
-// @public
-export class QueryDocumentSnapshot<T = DocumentData> extends DocumentSnapshot<T> {
-    // @override
-    data(options?: SnapshotOptions): T;
-}
-
-// @public
-export function queryEqual<T>(left: Query<T>, right: Query<T>): boolean;
-
-// @public
-export class QuerySnapshot<T = DocumentData> {
-    docChanges(options?: SnapshotListenOptions): Array<DocumentChange<T>>;
-    get docs(): Array<QueryDocumentSnapshot<T>>;
-    get empty(): boolean;
-    forEach(callback: (result: QueryDocumentSnapshot<T>) => void, thisArg?: unknown): void;
-    readonly metadata: SnapshotMetadata;
-    readonly query: Query<T>;
-    get size(): number;
-}
-
-// @public
-export function refEqual<T>(left: DocumentReference<T> | CollectionReference<T>, right: DocumentReference<T> | CollectionReference<T>): boolean;
-
-// @public
-export function runTransaction<T>(firestore: Firestore, updateFunction: (transaction: Transaction) => Promise<T>): Promise<T>;
-
-// @public
-export function serverTimestamp(): FieldValue;
-
-// @public
-export function setDoc<T>(reference: DocumentReference<T>, data: WithFieldValue<T>): Promise<void>;
-
-// @public
-export function setDoc<T>(reference: DocumentReference<T>, data: PartialWithFieldValue<T>, options: SetOptions): Promise<void>;
-
-// @public
-export function setLogLevel(logLevel: LogLevel): void;
-
-// @public
-export type SetOptions = {
-    readonly merge?: boolean;
-} | {
-    readonly mergeFields?: Array<string | FieldPath>;
-};
-
-// @public
-export function snapshotEqual<T>(left: DocumentSnapshot<T> | QuerySnapshot<T>, right: DocumentSnapshot<T> | QuerySnapshot<T>): boolean;
-
-// @public
-export interface SnapshotListenOptions {
-    readonly includeMetadataChanges?: boolean;
-}
-
-// @public
-export class SnapshotMetadata {
-    readonly fromCache: boolean;
-    readonly hasPendingWrites: boolean;
-    isEqual(other: SnapshotMetadata): boolean;
-}
-
-// @public
-export interface SnapshotOptions {
-    readonly serverTimestamps?: 'estimate' | 'previous' | 'none';
-}
-
-// @public
-export function startAfter(snapshot: DocumentSnapshot<unknown>): QueryConstraint;
-
-// @public
-export function startAfter(...fieldValues: unknown[]): QueryConstraint;
-
-// @public
-export function startAt(snapshot: DocumentSnapshot<unknown>): QueryConstraint;
-
-// @public
-export function startAt(...fieldValues: unknown[]): QueryConstraint;
-
-// @public
-export type TaskState = 'Error' | 'Running' | 'Success';
-
-// @public
-export function terminate(firestore: Firestore): Promise<void>;
-
-// @public
-export class Timestamp {
-    constructor(
-    seconds: number,
-    nanoseconds: number);
-    static fromDate(date: Date): Timestamp;
-    static fromMillis(milliseconds: number): Timestamp;
-    isEqual(other: Timestamp): boolean;
-    readonly nanoseconds: number;
-    static now(): Timestamp;
-    readonly seconds: number;
-    toDate(): Date;
-    toJSON(): {
-        seconds: number;
-        nanoseconds: number;
-    };
-    toMillis(): number;
-    toString(): string;
-    valueOf(): string;
-}
-
-// @public
-export class Transaction {
-    delete(documentRef: DocumentReference<unknown>): this;
-    get<T>(documentRef: DocumentReference<T>): Promise<DocumentSnapshot<T>>;
-    set<T>(documentRef: DocumentReference<T>, data: WithFieldValue<T>): this;
-    set<T>(documentRef: DocumentReference<T>, data: PartialWithFieldValue<T>, options: SetOptions): this;
-    update<T>(documentRef: DocumentReference<T>, data: UpdateData<T>): this;
-    update(documentRef: DocumentReference<unknown>, field: string | FieldPath, value: unknown, ...moreFieldsAndValues: unknown[]): this;
-}
-
-// @public
-export type UnionToIntersection<U> = (U extends unknown ? (k: U) => void : never) extends (k: infer I) => void ? I : never;
-
-// @public
-export interface Unsubscribe {
-    (): void;
-}
-
-// @public
-export type UpdateData<T> = T extends Primitive ? T : T extends Map<infer K, infer V> ? Map<UpdateData<K>, UpdateData<V>> : T extends {} ? {
-    [K in keyof T]?: UpdateData<T[K]> | FieldValue;
-} & NestedUpdateFields<T> : Partial<T>;
-
-// @public
-export function updateDoc<T>(reference: DocumentReference<T>, data: UpdateData<T>): Promise<void>;
-
-// @public
-export function updateDoc(reference: DocumentReference<unknown>, field: string | FieldPath, value: unknown, ...moreFieldsAndValues: unknown[]): Promise<void>;
-
-// @public
-export function waitForPendingWrites(firestore: Firestore): Promise<void>;
-
-// @public
-export function where(fieldPath: string | FieldPath, opStr: WhereFilterOp, value: unknown): QueryConstraint;
-
-// @public
-export type WhereFilterOp = '<' | '<=' | '==' | '!=' | '>=' | '>' | 'array-contains' | 'in' | 'array-contains-any' | 'not-in';
-
-// @public
-export type WithFieldValue<T> = T extends Primitive ? T : T extends {} ? {
-    [K in keyof T]: WithFieldValue<T[K]> | FieldValue;
-} : Partial<T>;
-
-// @public
-export class WriteBatch {
-    commit(): Promise<void>;
-    delete(documentRef: DocumentReference<unknown>): WriteBatch;
-    set<T>(documentRef: DocumentReference<T>, data: WithFieldValue<T>): WriteBatch;
-    set<T>(documentRef: DocumentReference<T>, data: PartialWithFieldValue<T>, options: SetOptions): WriteBatch;
-    update<T>(documentRef: DocumentReference<T>, data: UpdateData<T>): WriteBatch;
-    update(documentRef: DocumentReference<unknown>, field: string | FieldPath, value: unknown, ...moreFieldsAndValues: unknown[]): WriteBatch;
-}
-
-// @public
-export function writeBatch(firestore: Firestore): WriteBatch;
-
-
-```
+## API Report File for "@firebase/firestore"
+
+> Do not edit this file. It is a report generated by [API Extractor](https://api-extractor.com/).
+
+```ts
+
+import { EmulatorMockTokenOptions } from '@firebase/util';
+import { FirebaseApp } from '@firebase/app';
+import { LogLevelString as LogLevel } from '@firebase/logger';
+
+// @public
+export function addDoc<T>(reference: CollectionReference<T>, data: WithFieldValue<T>): Promise<DocumentReference<T>>;
+
+// @public
+export type AddPrefixToKeys<Prefix extends string, T extends Record<string, unknown>> = {
+    [K in keyof T & string as `${Prefix}.${K}`]+?: T[K];
+};
+
+// @public
+export function arrayRemove(...elements: unknown[]): FieldValue;
+
+// @public
+export function arrayUnion(...elements: unknown[]): FieldValue;
+
+// @public
+export class Bytes {
+    static fromBase64String(base64: string): Bytes;
+    static fromUint8Array(array: Uint8Array): Bytes;
+    isEqual(other: Bytes): boolean;
+    toBase64(): string;
+    toString(): string;
+    toUint8Array(): Uint8Array;
+}
+
+// @public
+export const CACHE_SIZE_UNLIMITED = -1;
+
+// @public
+export type ChildUpdateFields<K extends string, V> = V extends Record<string, unknown> ? AddPrefixToKeys<K, UpdateData<V>> : never;
+
+// @public
+export function clearIndexedDbPersistence(firestore: Firestore): Promise<void>;
+
+// @public
+export function collection(firestore: Firestore, path: string, ...pathSegments: string[]): CollectionReference<DocumentData>;
+
+// @public
+export function collection(reference: CollectionReference<unknown>, path: string, ...pathSegments: string[]): CollectionReference<DocumentData>;
+
+// @public
+export function collection(reference: DocumentReference, path: string, ...pathSegments: string[]): CollectionReference<DocumentData>;
+
+// @public
+export function collectionGroup(firestore: Firestore, collectionId: string): Query<DocumentData>;
+
+// @public
+export class CollectionReference<T = DocumentData> extends Query<T> {
+    get id(): string;
+    get parent(): DocumentReference<DocumentData> | null;
+    get path(): string;
+    readonly type = "collection";
+    withConverter<U>(converter: FirestoreDataConverter<U>): CollectionReference<U>;
+    withConverter(converter: null): CollectionReference<DocumentData>;
+}
+
+// @public
+export function connectFirestoreEmulator(firestore: Firestore, host: string, port: number, options?: {
+    mockUserToken?: EmulatorMockTokenOptions | string;
+}): void;
+
+// @public
+export function deleteDoc(reference: DocumentReference<unknown>): Promise<void>;
+
+// @public
+export function deleteField(): FieldValue;
+
+// @public
+export function disableNetwork(firestore: Firestore): Promise<void>;
+
+// @public
+export function doc(firestore: Firestore, path: string, ...pathSegments: string[]): DocumentReference<DocumentData>;
+
+// @public
+export function doc<T>(reference: CollectionReference<T>, path?: string, ...pathSegments: string[]): DocumentReference<T>;
+
+// @public
+export function doc(reference: DocumentReference<unknown>, path: string, ...pathSegments: string[]): DocumentReference<DocumentData>;
+
+// @public
+export interface DocumentChange<T = DocumentData> {
+    readonly doc: QueryDocumentSnapshot<T>;
+    readonly newIndex: number;
+    readonly oldIndex: number;
+    readonly type: DocumentChangeType;
+}
+
+// @public
+export type DocumentChangeType = 'added' | 'removed' | 'modified';
+
+// @public
+export interface DocumentData {
+    [field: string]: any;
+}
+
+// @public
+export function documentId(): FieldPath;
+
+// @public
+export class DocumentReference<T = DocumentData> {
+    readonly converter: FirestoreDataConverter<T> | null;
+    readonly firestore: Firestore;
+    get id(): string;
+    get parent(): CollectionReference<T>;
+    get path(): string;
+    readonly type = "document";
+    withConverter<U>(converter: FirestoreDataConverter<U>): DocumentReference<U>;
+    withConverter(converter: null): DocumentReference<DocumentData>;
+}
+
+// @public
+export class DocumentSnapshot<T = DocumentData> {
+    protected constructor();
+    data(options?: SnapshotOptions): T | undefined;
+    exists(): this is QueryDocumentSnapshot<T>;
+    get(fieldPath: string | FieldPath, options?: SnapshotOptions): any;
+    get id(): string;
+    readonly metadata: SnapshotMetadata;
+    get ref(): DocumentReference<T>;
+}
+
+export { EmulatorMockTokenOptions }
+
+// @public
+export function enableIndexedDbPersistence(firestore: Firestore, persistenceSettings?: PersistenceSettings): Promise<void>;
+
+// @public
+export function enableMultiTabIndexedDbPersistence(firestore: Firestore): Promise<void>;
+
+// @public
+export function enableNetwork(firestore: Firestore): Promise<void>;
+
+// @public
+export function endAt(snapshot: DocumentSnapshot<unknown>): QueryConstraint;
+
+// @public
+export function endAt(...fieldValues: unknown[]): QueryConstraint;
+
+// @public
+export function endBefore(snapshot: DocumentSnapshot<unknown>): QueryConstraint;
+
+// @public
+export function endBefore(...fieldValues: unknown[]): QueryConstraint;
+
+// @public
+export class FieldPath {
+    constructor(...fieldNames: string[]);
+    isEqual(other: FieldPath): boolean;
+}
+
+// @public
+export abstract class FieldValue {
+    abstract isEqual(other: FieldValue): boolean;
+}
+
+// @public
+export class Firestore {
+    get app(): FirebaseApp;
+    toJSON(): object;
+    type: 'firestore-lite' | 'firestore';
+}
+
+// @public
+export interface FirestoreDataConverter<T> {
+    fromFirestore(snapshot: QueryDocumentSnapshot<DocumentData>, options?: SnapshotOptions): T;
+    toFirestore(modelObject: WithFieldValue<T>): DocumentData;
+    toFirestore(modelObject: PartialWithFieldValue<T>, options: SetOptions): DocumentData;
+}
+
+// @public
+export class FirestoreError extends Error {
+    readonly code: FirestoreErrorCode;
+    readonly message: string;
+    readonly name: string;
+    readonly stack?: string;
+}
+
+// @public
+export type FirestoreErrorCode = 'cancelled' | 'unknown' | 'invalid-argument' | 'deadline-exceeded' | 'not-found' | 'already-exists' | 'permission-denied' | 'resource-exhausted' | 'failed-precondition' | 'aborted' | 'out-of-range' | 'unimplemented' | 'internal' | 'unavailable' | 'data-loss' | 'unauthenticated';
+
+// @public
+export interface FirestoreSettings {
+    cacheSizeBytes?: number;
+    experimentalAutoDetectLongPolling?: boolean;
+    experimentalForceLongPolling?: boolean;
+    host?: string;
+    ignoreUndefinedProperties?: boolean;
+    ssl?: boolean;
+}
+
+// @public
+export class GeoPoint {
+    constructor(latitude: number, longitude: number);
+    isEqual(other: GeoPoint): boolean;
+    get latitude(): number;
+    get longitude(): number;
+    toJSON(): {
+        latitude: number;
+        longitude: number;
+    };
+}
+
+// @public
+export function getDoc<T>(reference: DocumentReference<T>): Promise<DocumentSnapshot<T>>;
+
+// @public
+export function getDocFromCache<T>(reference: DocumentReference<T>): Promise<DocumentSnapshot<T>>;
+
+// @public
+export function getDocFromServer<T>(reference: DocumentReference<T>): Promise<DocumentSnapshot<T>>;
+
+// @public
+export function getDocs<T>(query: Query<T>): Promise<QuerySnapshot<T>>;
+
+// @public
+export function getDocsFromCache<T>(query: Query<T>): Promise<QuerySnapshot<T>>;
+
+// @public
+export function getDocsFromServer<T>(query: Query<T>): Promise<QuerySnapshot<T>>;
+
+// @public
+export function getFirestore(app?: FirebaseApp): Firestore;
+
+// @public
+export function increment(n: number): FieldValue;
+
+// @public
+export function initializeFirestore(app: FirebaseApp, settings: FirestoreSettings): Firestore;
+
+// @public
+export function limit(limit: number): QueryConstraint;
+
+// @public
+export function limitToLast(limit: number): QueryConstraint;
+
+// @public
+export function loadBundle(firestore: Firestore, bundleData: ReadableStream<Uint8Array> | ArrayBuffer | string): LoadBundleTask;
+
+// @public
+export class LoadBundleTask implements PromiseLike<LoadBundleTaskProgress> {
+    catch<R>(onRejected: (a: Error) => R | PromiseLike<R>): Promise<R | LoadBundleTaskProgress>;
+    onProgress(next?: (progress: LoadBundleTaskProgress) => unknown, error?: (err: Error) => unknown, complete?: () => void): void;
+    then<T, R>(onFulfilled?: (a: LoadBundleTaskProgress) => T | PromiseLike<T>, onRejected?: (a: Error) => R | PromiseLike<R>): Promise<T | R>;
+}
+
+// @public
+export interface LoadBundleTaskProgress {
+    bytesLoaded: number;
+    documentsLoaded: number;
+    taskState: TaskState;
+    totalBytes: number;
+    totalDocuments: number;
+}
+
+export { LogLevel }
+
+// @public
+export function namedQuery(firestore: Firestore, name: string): Promise<Query | null>;
+
+// @public
+export type NestedUpdateFields<T extends Record<string, unknown>> = UnionToIntersection<{
+    [K in keyof T & string]: ChildUpdateFields<K, T[K]>;
+}[keyof T & string]>;
+
+// @public
+export function onSnapshot<T>(reference: DocumentReference<T>, observer: {
+    next?: (snapshot: DocumentSnapshot<T>) => void;
+    error?: (error: FirestoreError) => void;
+    complete?: () => void;
+}): Unsubscribe;
+
+// @public
+export function onSnapshot<T>(reference: DocumentReference<T>, options: SnapshotListenOptions, observer: {
+    next?: (snapshot: DocumentSnapshot<T>) => void;
+    error?: (error: FirestoreError) => void;
+    complete?: () => void;
+}): Unsubscribe;
+
+// @public
+export function onSnapshot<T>(reference: DocumentReference<T>, onNext: (snapshot: DocumentSnapshot<T>) => void, onError?: (error: FirestoreError) => void, onCompletion?: () => void): Unsubscribe;
+
+// @public
+export function onSnapshot<T>(reference: DocumentReference<T>, options: SnapshotListenOptions, onNext: (snapshot: DocumentSnapshot<T>) => void, onError?: (error: FirestoreError) => void, onCompletion?: () => void): Unsubscribe;
+
+// @public
+export function onSnapshot<T>(query: Query<T>, observer: {
+    next?: (snapshot: QuerySnapshot<T>) => void;
+    error?: (error: FirestoreError) => void;
+    complete?: () => void;
+}): Unsubscribe;
+
+// @public
+export function onSnapshot<T>(query: Query<T>, options: SnapshotListenOptions, observer: {
+    next?: (snapshot: QuerySnapshot<T>) => void;
+    error?: (error: FirestoreError) => void;
+    complete?: () => void;
+}): Unsubscribe;
+
+// @public
+export function onSnapshot<T>(query: Query<T>, onNext: (snapshot: QuerySnapshot<T>) => void, onError?: (error: FirestoreError) => void, onCompletion?: () => void): Unsubscribe;
+
+// @public
+export function onSnapshot<T>(query: Query<T>, options: SnapshotListenOptions, onNext: (snapshot: QuerySnapshot<T>) => void, onError?: (error: FirestoreError) => void, onCompletion?: () => void): Unsubscribe;
+
+// @public
+export function onSnapshotsInSync(firestore: Firestore, observer: {
+    next?: (value: void) => void;
+    error?: (error: FirestoreError) => void;
+    complete?: () => void;
+}): Unsubscribe;
+
+// @public
+export function onSnapshotsInSync(firestore: Firestore, onSync: () => void): Unsubscribe;
+
+// @public
+export function orderBy(fieldPath: string | FieldPath, directionStr?: OrderByDirection): QueryConstraint;
+
+// @public
+export type OrderByDirection = 'desc' | 'asc';
+
+// @public
+export type PartialWithFieldValue<T> = T extends Primitive ? T : T extends {} ? {
+    [K in keyof T]?: PartialWithFieldValue<T[K]> | FieldValue;
+} : Partial<T>;
+
+// @public
+export interface PersistenceSettings {
+    forceOwnership?: boolean;
+}
+
+// @public
+export type Primitive = string | number | boolean | undefined | null;
+
+// @public
+export class Query<T = DocumentData> {
+    protected constructor();
+    readonly converter: FirestoreDataConverter<T> | null;
+    readonly firestore: Firestore;
+    readonly type: 'query' | 'collection';
+    withConverter(converter: null): Query<DocumentData>;
+    withConverter<U>(converter: FirestoreDataConverter<U>): Query<U>;
+}
+
+// @public
+export function query<T>(query: Query<T>, ...queryConstraints: QueryConstraint[]): Query<T>;
+
+// @public
+export abstract class QueryConstraint {
+    abstract readonly type: QueryConstraintType;
+}
+
+// @public
+export type QueryConstraintType = 'where' | 'orderBy' | 'limit' | 'limitToLast' | 'startAt' | 'startAfter' | 'endAt' | 'endBefore';
+
+// @public
+export class QueryDocumentSnapshot<T = DocumentData> extends DocumentSnapshot<T> {
+    // @override
+    data(options?: SnapshotOptions): T;
+}
+
+// @public
+export function queryEqual<T>(left: Query<T>, right: Query<T>): boolean;
+
+// @public
+export class QuerySnapshot<T = DocumentData> {
+    docChanges(options?: SnapshotListenOptions): Array<DocumentChange<T>>;
+    get docs(): Array<QueryDocumentSnapshot<T>>;
+    get empty(): boolean;
+    forEach(callback: (result: QueryDocumentSnapshot<T>) => void, thisArg?: unknown): void;
+    readonly metadata: SnapshotMetadata;
+    readonly query: Query<T>;
+    get size(): number;
+}
+
+// @public
+export function refEqual<T>(left: DocumentReference<T> | CollectionReference<T>, right: DocumentReference<T> | CollectionReference<T>): boolean;
+
+// @public
+export function runTransaction<T>(firestore: Firestore, updateFunction: (transaction: Transaction) => Promise<T>): Promise<T>;
+
+// @public
+export function serverTimestamp(): FieldValue;
+
+// @public
+export function setDoc<T>(reference: DocumentReference<T>, data: WithFieldValue<T>): Promise<void>;
+
+// @public
+export function setDoc<T>(reference: DocumentReference<T>, data: PartialWithFieldValue<T>, options: SetOptions): Promise<void>;
+
+// @public
+export function setLogLevel(logLevel: LogLevel): void;
+
+// @public
+export type SetOptions = {
+    readonly merge?: boolean;
+} | {
+    readonly mergeFields?: Array<string | FieldPath>;
+};
+
+// @public
+export function snapshotEqual<T>(left: DocumentSnapshot<T> | QuerySnapshot<T>, right: DocumentSnapshot<T> | QuerySnapshot<T>): boolean;
+
+// @public
+export interface SnapshotListenOptions {
+    readonly includeMetadataChanges?: boolean;
+}
+
+// @public
+export class SnapshotMetadata {
+    readonly fromCache: boolean;
+    readonly hasPendingWrites: boolean;
+    isEqual(other: SnapshotMetadata): boolean;
+}
+
+// @public
+export interface SnapshotOptions {
+    readonly serverTimestamps?: 'estimate' | 'previous' | 'none';
+}
+
+// @public
+export function startAfter(snapshot: DocumentSnapshot<unknown>): QueryConstraint;
+
+// @public
+export function startAfter(...fieldValues: unknown[]): QueryConstraint;
+
+// @public
+export function startAt(snapshot: DocumentSnapshot<unknown>): QueryConstraint;
+
+// @public
+export function startAt(...fieldValues: unknown[]): QueryConstraint;
+
+// @public
+export type TaskState = 'Error' | 'Running' | 'Success';
+
+// @public
+export function terminate(firestore: Firestore): Promise<void>;
+
+// @public
+export class Timestamp {
+    constructor(
+    seconds: number,
+    nanoseconds: number);
+    static fromDate(date: Date): Timestamp;
+    static fromMillis(milliseconds: number): Timestamp;
+    isEqual(other: Timestamp): boolean;
+    readonly nanoseconds: number;
+    static now(): Timestamp;
+    readonly seconds: number;
+    toDate(): Date;
+    toJSON(): {
+        seconds: number;
+        nanoseconds: number;
+    };
+    toMillis(): number;
+    toString(): string;
+    valueOf(): string;
+}
+
+// @public
+export class Transaction {
+    delete(documentRef: DocumentReference<unknown>): this;
+    get<T>(documentRef: DocumentReference<T>): Promise<DocumentSnapshot<T>>;
+    set<T>(documentRef: DocumentReference<T>, data: WithFieldValue<T>): this;
+    set<T>(documentRef: DocumentReference<T>, data: PartialWithFieldValue<T>, options: SetOptions): this;
+    update<T>(documentRef: DocumentReference<T>, data: UpdateData<T>): this;
+    update(documentRef: DocumentReference<unknown>, field: string | FieldPath, value: unknown, ...moreFieldsAndValues: unknown[]): this;
+}
+
+// @public
+export type UnionToIntersection<U> = (U extends unknown ? (k: U) => void : never) extends (k: infer I) => void ? I : never;
+
+// @public
+export interface Unsubscribe {
+    (): void;
+}
+
+// @public
+export type UpdateData<T> = T extends Primitive ? T : T extends {} ? {
+    [K in keyof T]?: UpdateData<T[K]> | FieldValue;
+} & NestedUpdateFields<T> : Partial<T>;
+
+// @public
+export function updateDoc<T>(reference: DocumentReference<T>, data: UpdateData<T>): Promise<void>;
+
+// @public
+export function updateDoc(reference: DocumentReference<unknown>, field: string | FieldPath, value: unknown, ...moreFieldsAndValues: unknown[]): Promise<void>;
+
+// @public
+export function waitForPendingWrites(firestore: Firestore): Promise<void>;
+
+// @public
+export function where(fieldPath: string | FieldPath, opStr: WhereFilterOp, value: unknown): QueryConstraint;
+
+// @public
+export type WhereFilterOp = '<' | '<=' | '==' | '!=' | '>=' | '>' | 'array-contains' | 'in' | 'array-contains-any' | 'not-in';
+
+// @public
+export type WithFieldValue<T> = T extends Primitive ? T : T extends {} ? {
+    [K in keyof T]: WithFieldValue<T[K]> | FieldValue;
+} : Partial<T>;
+
+// @public
+export class WriteBatch {
+    commit(): Promise<void>;
+    delete(documentRef: DocumentReference<unknown>): WriteBatch;
+    set<T>(documentRef: DocumentReference<T>, data: WithFieldValue<T>): WriteBatch;
+    set<T>(documentRef: DocumentReference<T>, data: PartialWithFieldValue<T>, options: SetOptions): WriteBatch;
+    update<T>(documentRef: DocumentReference<T>, data: UpdateData<T>): WriteBatch;
+    update(documentRef: DocumentReference<unknown>, field: string | FieldPath, value: unknown, ...moreFieldsAndValues: unknown[]): WriteBatch;
+}
+
+// @public
+export function writeBatch(firestore: Firestore): WriteBatch;
+
+
+```
diff --git a/packages/firestore/lite/index.ts b/packages/firestore/lite/index.ts
index 81f7318ec2a..42e1554c92e 100644
--- a/packages/firestore/lite/index.ts
+++ b/packages/firestore/lite/index.ts
@@ -82,6 +82,7 @@ export {
 export {
   Primitive,
   NestedUpdateFields,
+  ChildUpdateFields,
   AddPrefixToKeys,
   UnionToIntersection
 } from '../src/lite-api/types';
diff --git a/packages/firestore/src/api.ts b/packages/firestore/src/api.ts
index 96af005ad48..b20bf1b9ae6 100644
--- a/packages/firestore/src/api.ts
+++ b/packages/firestore/src/api.ts
@@ -136,6 +136,7 @@ export { AbstractUserDataWriter } from './lite-api/user_data_writer';
 export {
   Primitive,
   NestedUpdateFields,
+  ChildUpdateFields,
   AddPrefixToKeys,
   UnionToIntersection
 } from '../src/lite-api/types';
diff --git a/packages/firestore/src/lite-api/reference.ts b/packages/firestore/src/lite-api/reference.ts
index 50e6d9a652c..0b63d5fe2a3 100644
--- a/packages/firestore/src/lite-api/reference.ts
+++ b/packages/firestore/src/lite-api/reference.ts
@@ -78,12 +78,9 @@ export type WithFieldValue<T> = T extends Primitive
  */
 export type UpdateData<T> = T extends Primitive
   ? T
-  : T extends Map<infer K, infer V>
-  ? Map<UpdateData<K>, UpdateData<V>>
   : T extends {}
   ? { [K in keyof T]?: UpdateData<T[K]> | FieldValue } & NestedUpdateFields<T>
   : Partial<T>;
-
 /**
  * An options object that configures the behavior of {@link @firebase/firestore/lite#(setDoc:1)}, {@link
  * @firebase/firestore/lite#(WriteBatch.set:1)} and {@link @firebase/firestore/lite#(Transaction.set:1)} calls. These calls can be
diff --git a/packages/firestore/src/lite-api/types.ts b/packages/firestore/src/lite-api/types.ts
index 63d1b1cc752..4801e587836 100644
--- a/packages/firestore/src/lite-api/types.ts
+++ b/packages/firestore/src/lite-api/types.ts
@@ -34,16 +34,29 @@ export type Primitive = string | number | boolean | undefined | null;
 export type NestedUpdateFields<T extends Record<string, unknown>> =
   UnionToIntersection<
     {
-      // Check that T[K] extends Record to only allow nesting for map values.
-      [K in keyof T & string]: T[K] extends Record<string, unknown>
-        ? // Recurse into the map and add the prefix in front of each key
-          // (e.g. Prefix 'bar.' to create: 'bar.baz' and 'bar.qux'.
-          AddPrefixToKeys<K, UpdateData<T[K]>>
-        : // TypedUpdateData is always a map of values.
-          never;
+      [K in keyof T & string]: ChildUpdateFields<K, T[K]>;
     }[keyof T & string] // Also include the generated prefix-string keys.
   >;
 
+/**
+ * Helper for calculating the nested fields for a given type T1. This is needed
+ * to distribute union types such as `undefined | {...}` (happens for optional
+ * props) or `{a: A} | {b: B}`.
+ *
+ * In this use case, `V` is used to distribute the union types of `T[K]` on
+ * `Record`, since `T[K]` is evaluated as an expression and not distributed.
+ *
+ * See https://www.typescriptlang.org/docs/handbook/advanced-types.html#distributive-conditional-types
+ */
+export type ChildUpdateFields<K extends string, V> =
+  // Only allow nesting for map values
+  V extends Record<string, unknown>
+    ? // Recurse into the map and add the prefix in front of each key
+      // (e.g. Prefix 'bar.' to create: 'bar.baz' and 'bar.qux'.
+      AddPrefixToKeys<K, UpdateData<V>>
+    : // UpdateData is always a map of values.
+      never;
+
 /**
  * Returns a new map where every key is prefixed with the outer key appended
  * to a dot.
diff --git a/packages/firestore/test/lite/integration.test.ts b/packages/firestore/test/lite/integration.test.ts
index a5035d58d3b..a9ebcbcf50b 100644
--- a/packages/firestore/test/lite/integration.test.ts
+++ b/packages/firestore/test/lite/integration.test.ts
@@ -1542,6 +1542,141 @@ describe('withConverter() support', () => {
         });
       });
 
+      it('supports optional fields', () => {
+        interface TestObjectOptional {
+          optionalStr?: string;
+          nested?: {
+            requiredStr: string;
+          };
+        }
+
+        const testConverterOptional = {
+          toFirestore(testObj: WithFieldValue<TestObjectOptional>) {
+            return { ...testObj };
+          },
+          fromFirestore(snapshot: QueryDocumentSnapshot): TestObjectOptional {
+            const data = snapshot.data();
+            return {
+              optionalStr: data.optionalStr,
+              nested: data.nested
+            };
+          }
+        };
+
+        return withTestDocAndInitialData(initialData, async docRef => {
+          const testDocRef: DocumentReference<TestObjectOptional> =
+            docRef.withConverter(testConverterOptional);
+
+          await updateDoc(testDocRef, {
+            optionalStr: 'foo'
+          });
+          await updateDoc(testDocRef, {
+            'optionalStr': 'foo'
+          });
+
+          await updateDoc(testDocRef, {
+            nested: {
+              requiredStr: 'foo'
+            }
+          });
+          await updateDoc(testDocRef, {
+            'nested.requiredStr': 'foo'
+          });
+        });
+      });
+
+      it('supports null fields', () => {
+        interface TestObjectOptional {
+          optionalStr?: string;
+          nested?: {
+            strOrNull: string | null;
+          };
+        }
+
+        const testConverterOptional = {
+          toFirestore(testObj: WithFieldValue<TestObjectOptional>) {
+            return { ...testObj };
+          },
+          fromFirestore(snapshot: QueryDocumentSnapshot): TestObjectOptional {
+            const data = snapshot.data();
+            return {
+              optionalStr: data.optionalStr,
+              nested: data.nested
+            };
+          }
+        };
+
+        return withTestDocAndInitialData(initialData, async docRef => {
+          const testDocRef: DocumentReference<TestObjectOptional> =
+            docRef.withConverter(testConverterOptional);
+
+          await updateDoc(testDocRef, {
+            nested: {
+              strOrNull: null
+            }
+          });
+          await updateDoc(testDocRef, {
+            'nested.strOrNull': null
+          });
+        });
+      });
+
+      it('supports union fields', () => {
+        interface TestObjectUnion {
+          optionalStr?: string;
+          nested?:
+            | {
+                requiredStr: string;
+              }
+            | { requiredNumber: number };
+        }
+
+        const testConverterUnion = {
+          toFirestore(testObj: WithFieldValue<TestObjectUnion>) {
+            return { ...testObj };
+          },
+          fromFirestore(snapshot: QueryDocumentSnapshot): TestObjectUnion {
+            const data = snapshot.data();
+            return {
+              optionalStr: data.optionalStr,
+              nested: data.nested
+            };
+          }
+        };
+
+        return withTestDocAndInitialData(initialData, async docRef => {
+          const testDocRef: DocumentReference<TestObjectUnion> =
+            docRef.withConverter(testConverterUnion);
+
+          await updateDoc(testDocRef, {
+            nested: {
+              requiredStr: 'foo'
+            }
+          });
+
+          await updateDoc(testDocRef, {
+            'nested.requiredStr': 'foo'
+          });
+          await updateDoc(testDocRef, {
+            // @ts-expect-error
+            'nested.requiredStr': 1
+          });
+
+          await updateDoc(testDocRef, {
+            'nested.requiredNumber': 1
+          });
+
+          await updateDoc(testDocRef, {
+            // @ts-expect-error
+            'nested.requiredNumber': 'foo'
+          });
+          await updateDoc(testDocRef, {
+            // @ts-expect-error
+            'nested.requiredNumber': null
+          });
+        });
+      });
+
       it('checks for nonexistent fields', () => {
         return withTestDocAndInitialData(initialData, async docRef => {
           const testDocRef: DocumentReference<TestObject> =