问RxJS -告诉可观察到的其他可观察到的发出非空值

EN

public set mappedItem(mappedItem: IPermissionsMappedItem) {
    mappedItem.hydrate$Permissions().then(_ => {
        this.mappedItem$.next(mappedItem);
        this.systemAreasOptions$ = from(
            this.lookupService.SYSTEM_AREAS.toNestedLookup()
                .$promise as unknown as Observable<IPermissmissionsLookup[]>
        ).pipe(
            map(systemAreas => orderBy(systemAreas,systemArea => systemArea?.label?.toLowerCase())),
            map(systemAreas => systemAreas.map(area => ({
                ...area,
                permissions: this.getPermissionsForArea(area.id)
            }))),
            shareReplay(1),
            tap(console.log)
        );

        this._subscriptions.add(
            this.systemAreasOptions$.subscribe(
                this.systemAreasOptionsBehaviourSubject$)
        );
    });
}