feat(rxjs-core): mapAndCacheArrayElements() handles null and undefined

projects/rxjs-core/src/lib/operators/map-and-cache-array-elements.spec.ts

@@ -111,6 +111,14 @@ describe('mapAndCacheArrayElements()', () => {
     }
   });
 
+  it('treats null and undefined like the empty array', async () => {
+    await expectPipeResult<number[] | null | undefined, number[]>(
+      [null, [1, 2], undefined],
+      mapAndCacheArrayElements(identity, (item) => item * 3),
+      [[], [3, 6], []],
+    );
+  });
+
   it(
     'handles `buildCacheKey` throwing an error',
     testUserFunctionError(

projects/rxjs-core/src/lib/operators/map-and-cache-array-elements.ts

@@ -28,4 +28,4 @@ export const mapAndCacheArrayElements = mapAndCacheElements as <
 >(
   buildCacheKey: ArrayIteratee<UpstreamType, any>,
   buildDownstreamItem: ArrayIteratee<UpstreamType, DownstreamType>,
-) => OperatorFunction<UpstreamType[], DownstreamType[]>;
+) => OperatorFunction<UpstreamType[] | null | undefined, DownstreamType[]>;

projects/rxjs-core/src/typing-tests/map-and-cache-array-elements.dts-spec.ts

@@ -0,0 +1,49 @@
+import { identity } from '@s-libs/micro-dash';
+import { Subject } from 'rxjs';
+import { mapAndCacheArrayElements } from '../lib/operators';
+
+declare const array: Subject<number[]>;
+declare const arrayOrNull: Subject<number[] | null>;
+declare const arrayOrUndefined: Subject<number[] | undefined>;
+declare const arrayOrNil: Subject<number[] | null | undefined>;
+
+// $ExpectType Observable<Date[]>
+array.pipe(
+  mapAndCacheArrayElements(
+    identity,
+    (
+      // $ExpectType number
+      val,
+    ) => new Date(val),
+  ),
+);
+// $ExpectType Observable<Date[]>
+arrayOrNull.pipe(
+  mapAndCacheArrayElements(
+    identity,
+    (
+      // $ExpectType number
+      val,
+    ) => new Date(val),
+  ),
+);
+// $ExpectType Observable<Date[]>
+arrayOrUndefined.pipe(
+  mapAndCacheArrayElements(
+    identity,
+    (
+      // $ExpectType number
+      val,
+    ) => new Date(val),
+  ),
+);
+// $ExpectType Observable<Date[]>
+arrayOrNil.pipe(
+  mapAndCacheArrayElements(
+    identity,
+    (
+      // $ExpectType number
+      val,
+    ) => new Date(val),
+  ),
+);