我正在写一个注册入口点，它想返回一个带有id和token的dto。我试过在控制器中使用flatmap代替map，但是结果是一样的。代码有两部分，第一部分是注册（用于保存和检查用户），第二部分（查找用户id）。但是我的问题是如何Map结果，这涉及到两个单变量。
代码：

@PostMapping("/signup")
public Mono<AuthResponse> signup(@RequestBody user_info user) {
    return tokenService.signup(user)
            .doOnNext(System.out::println)
            .switchIfEmpty(Mono.error(new Error("signup not work")))
            .flatMap(token->{
                return userRespository.findByyUsername(user.getUsername())
                        .doOnNext(System.out::println)
                        .switchIfEmpty(Mono.error(new Error("finding fail")))
                        .flatMap(userInfo ->
                                Mono.just(new AuthResponse(userInfo.getId(),token)));
            });

验证响应：（日期至）

@Data
@AllArgsConstructor
public class AuthResponse {
    private Integer id;
    private String token;
}

错误输出：

2023-02-05T02:45:41.539+08:00 ERROR 147274 --- [tor-tcp-epoll-2] a.w.r.e.AbstractErrorWebExceptionHandler : [c841e0d1-1]  500 Server Error for HTTP POST "/signup"

java.lang.Error: finding fail
    at com.springboot.sohinalex.java.Controller.apigatewayController.lambda$signup$1(apigatewayController.java:51) ~[classes/:na]
    Suppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException: 
Error has been observed at the following site(s):
    *__checkpoint ⇢ Handler com.springboot.sohinalex.java.Controller.apigatewayController#signup(user_info) [DispatcherHandler]
    *__checkpoint ⇢ org.springframework.cloud.gateway.filter.WeightCalculatorWebFilter [DefaultWebFilterChain]
    *__checkpoint ⇢ org.springframework.security.web.server.authorization.AuthorizationWebFilter [DefaultWebFilterChain]
    *__checkpoint ⇢ org.springframework.security.web.server.authorization.ExceptionTranslationWebFilter [DefaultWebFilterChain]
    *__checkpoint ⇢ org.springframework.security.web.server.authentication.logout.LogoutWebFilter [DefaultWebFilterChain]
    *__checkpoint ⇢ org.springframework.security.web.server.savedrequest.ServerRequestCacheWebFilter [DefaultWebFilterChain]
    *__checkpoint ⇢ org.springframework.security.web.server.context.SecurityContextServerWebExchangeWebFilter [DefaultWebFilterChain]
    *__checkpoint ⇢ org.springframework.security.web.server.authentication.AuthenticationWebFilter [DefaultWebFilterChain]
    *__checkpoint ⇢ org.springframework.security.web.server.authentication.AuthenticationWebFilter [DefaultWebFilterChain]
    *__checkpoint ⇢ org.springframework.security.web.server.context.ReactorContex

供参考：注册功能：

public Mono<String> signup(user_info user)  {

            log.info("signup start");
            return Mono.just(user).doOnNext(System.out::println)
                    .switchIfEmpty(Mono.error(new RuntimeException()))
                         .flatMap(Monouser->{
                     Mono<Boolean> isuserexist=IsUsernameExist(Monouser.getUsername())
                             .doOnNext(System.out::println)
                             .switchIfEmpty(Mono.just(false))  //no user found => can register
                             .mapNotNull(res-> res
                             );
                     Monouser.setPassword(  //encode the password
                                     passwordEncoder.encode(user.getPassword()));
                     Mono<user_info> savedusr = respository.save(
                     Monouser).log();

                            return isuserexist.doOnNext(System.out::println) //check the username exist in my db
                                    .switchIfEmpty(Mono.error(new RuntimeException()))
                                    .flatMap(
                                    res->{
                                        log.info("start the map");
                                        if(res){
                                        log.info("error");
                                        return null;
                                    }
                                    else {
                                            savedusr.subscribe();//execute the saving user
                                            log.info("check");
                                       return  reactiveAuthenticationManager.authenticate(
                                                new UsernamePasswordAuthenticationToken(
                                                        user.getUsername(),user.getPassword()
                                                )
                                        ).map(this::generateToken);

                                    }
                                    }
                            );