Support union types and optional fields with dot separation on UpdateData

.changeset/clean-cameras-check.md

@@ -0,0 +1,5 @@
+---
+'@firebase/firestore': minor
+---
+
+Fixed a bug where UpdateData did not recognize optional, dot-separated string fields

common/api-review/firestore-lite.api.md

@@ -191,7 +191,7 @@ 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]: T[K] extends Record<string, unknown> | undefined ? AddPrefixToKeys<K, UpdateData<T[K]>> : never;
 }[keyof T & string]>;
 
 // @public
@@ -332,7 +332,7 @@ 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 undefined ? never : T extends Primitive ? T : T extends {} ? {
     [K in keyof T]?: UpdateData<T[K]> | FieldValue;
 } & NestedUpdateFields<T> : Partial<T>;