Wanted to throw an exception using Reactive Spring only if username a new user wanted to have was being used for someone what was't him

ReactiveIf2.java

    private Mono<UserDto> validateUpdate(Long partyId, UserDto request) {
        return partyClient.getIndividual(partyId) 
                .flatMap(r -> securityClient.getByUserName(request.getUsername()))
                .switchIfEmpty(Mono.just(UserModel.builder().withId(partyId).build())) //dummy to have something to compare with and kee the reactive flow "flowing"
                .flatMap(r -> {
                    if (!r.getId().equals(partyId)) {
                        throw new UserAlreadyExistsException("Username already taken");
                    }
                    return Mono.just(request);
                }
        );
    }