fix(app-state): unsubscribing mid-emit could sometimes result in an e…

…rror

projects/app-state/src/lib/store.spec.ts

@@ -157,6 +157,19 @@ describe('Store', () => {
       store('counter').set(1);
       expectSingleCallAndReset(spy, 1);
     });
+
+    it('works when the last subscriber to a child store unsubscribes mid-emit (production bug)', () => {
+      store('counter')
+        .$.pipe(skip(1))
+        .subscribe(() => {
+          sub2.unsubscribe();
+        });
+      const sub2 = store('nested').$.subscribe();
+
+      expect(() => {
+        store('counter').set(1);
+      }).not.toThrowError();
+    });
   });
 
   describe('()', () => {

projects/app-state/src/lib/store.ts

@@ -160,7 +160,8 @@ export abstract class Store<T> extends CallableObject<GetSlice<T>> {
       }
     });
     forOwn(this.activeChildren, (children) => {
-      for (const child of children) {
+      // `children` can be undefined if emitting from a previous key caused removed all subscribers to this key
+      for (const child of children || []) {
         child.maybeEmit();
       }
     });