fix code coverage

Author: yaacovCR

src/execution/publisher.ts

@@ -123,15 +123,9 @@ export class Publisher<TSource extends Source, TIncremental, TPayload> {
 
       const parentContext = source.parentContext;
       // TODO: parentContext can never be undefined, but TS doesn't know that
-      if (parentContext === undefined) {
-        return;
-      }
-      const children = this.waitingByParent.get(parentContext);
+      const children = this.waitingByParent.get(parentContext!);
       // TODO: children can never be undefined, but TS doesn't know that
-      if (children === undefined) {
-        return;
-      }
-      children.delete(source);
+      children!.delete(source);
     });
 
     for (const iterator of iterators) {