WebFlux函数:如何检测一个空的通量并返回404？

import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

@RestController
public class MyController {

    @GetMapping("/data")
    public Mono<ResponseEntity<String>> getData() {
        Flux<String> dataFlux = getDataFlux(); // 假设这是从某个地方获取的数据通量

        return dataFlux
                .collectList() // 将通量收集为一个列表
                .flatMap(dataList -> {
                    if (dataList.isEmpty()) {
                        return Mono.just(ResponseEntity.status(HttpStatus.NOT_FOUND).body("Data not found"));
                    } else {
                        return Mono.just(ResponseEntity.ok(dataList));
                    }
                });
    }

    private Flux<String> getDataFlux() {
        // 模拟一个空的通量
        return Flux.empty();
    }
}