Update LiveMap.get to always return undefined value as an option for keys that reference other LiveObjects

Referenced live objects can be not valid (haven't seen a create op) and
we should not surface such objects to the end user and return `undefined`
instead.

Author: VeskeR

ably.d.ts

@@ -2103,12 +2103,12 @@ export type DefaultRoot =
  */
 export declare interface LiveMap<T extends LiveMapType> extends LiveObject<LiveMapUpdate> {
   /**
-   * Returns the value associated with a given key. Returns `undefined` if the key doesn't exist in a map.
+   * Returns the value associated with a given key. Returns `undefined` if the key doesn't exist in a map or if the associated {@link LiveObject} has been deleted.
    *
    * @param key - The key to retrieve the value for.
-   * @returns A {@link LiveObject}, a primitive type (string, number, boolean, or binary data) or `undefined` if the key doesn't exist in a map.
+   * @returns A {@link LiveObject}, a primitive type (string, number, boolean, or binary data) or `undefined` if the key doesn't exist in a map or the associated {@link LiveObject} has been deleted.
    */
-  get<TKey extends keyof T & string>(key: TKey): T[TKey];
+  get<TKey extends keyof T & string>(key: TKey): T[TKey] extends StateValue ? T[TKey] : T[TKey] | undefined;
 
   /**
    * Returns the number of key/value pairs in the map.

src/plugins/liveobjects/livemap.ts

@@ -85,7 +85,7 @@ export class LiveMap<T extends API.LiveMapType> extends LiveObject<LiveMapData,
    * - If the value is not an objectId, then that value is returned.
    */
   // force the key to be of type string as we only allow strings as key in a map
-  get<TKey extends keyof T & string>(key: TKey): T[TKey] {
+  get<TKey extends keyof T & string>(key: TKey): T[TKey] extends StateValue ? T[TKey] : T[TKey] | undefined {
     const element = this._dataRef.data.get(key);
 
     if (element === undefined) {

test/package/browser/template/src/ably.config.d.ts

@@ -5,13 +5,13 @@ type CustomRoot = {
   stringKey: string;
   booleanKey: boolean;
   couldBeUndefined?: string;
-  mapKey?: LiveMap<{
+  mapKey: LiveMap<{
     foo: 'bar';
     nestedMap?: LiveMap<{
       baz: 'qux';
     }>;
   }>;
-  counterKey?: LiveCounter;
+  counterKey: LiveCounter;
 };
 
 declare global {

test/package/browser/template/src/index-liveobjects.ts

@@ -30,8 +30,10 @@ globalThis.testAblyPackage = async function () {
   const aBoolean: boolean = root.get('booleanKey');
   const couldBeUndefined: string | undefined = root.get('couldBeUndefined');
   // live objects on a root:
+  // LiveMap.get can still return undefined for LiveObject typed properties even if custom typings have them as non-optional.
+  // objects can be tombstoned/non-valid and result in the undefined value
   const counter: Ably.LiveCounter | undefined = root.get('counterKey');
-  const map: LiveObjectsTypes['root']['mapKey'] = root.get('mapKey');
+  const map: LiveObjectsTypes['root']['mapKey'] | undefined = root.get('mapKey');
   // check string literal types works
   // need to use nullish coalescing as we didn't actually create any data on the root,
   // so the next calls would fail. we only need to check that TypeScript types work