Webflux WebClient java.lang.NullPointerException

import org.springframework.web.reactive.function.client.WebClient;
import reactor.core.publisher.Mono;

public class WebClientExample {

    public static void main(String[] args) {
        WebClient webClient = WebClient.builder()
                .baseUrl("https://api.example.com")
                .build();

        Mono<String> responseMono = webClient.get()
                .uri("/data")
                .retrieve()
                .bodyToMono(String.class)
                .onErrorResume(e -> {
                    System.err.println("Error occurred: " + e.getMessage());
                    return Mono.empty();
                });

        responseMono.subscribe(
                response -> System.out.println("Response: " + response),
                error -> System.err.println("Subscriber error: " + error.getMessage())
        );
    }
}