UserStore - Property "user" is used before its initialization

export class UserStore {
private user: User = null;

protected userState$ = new BehaviorSubject(this.user);

angular 11/nebular 7 build gives error: UserStore - Property "user" is used before its initialization
previous versios gives only warning on build succees but on newer versions build faild on error.
I bought this code and it won't work!!!