我创建了一个空的asp.net core 项目，在这种情况下MapWhen方法里context的请求参数丢失了，不知道为什么会这样。
例如请求https://localhost:44369/maptest?bc=1，请求参数在MapWhen方法里丢失了

以下是代码，所有的请求只在Startup.Configure中处理

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        app.Use(next =>
        {
            return async c =>
            {
                await c.Response.WriteAsync(1 + "\r\n");
                await next(c);
            };
        });
       
        app.Map("/maptest", app1 =>
        {
            app1.Use(next =>
            {
                return async c =>
                {
                    await c.Response.WriteAsync("maptest" + "\r\n");
                    await next.Invoke(c);
                };
            });
            app1.Map("/ph1", app2 =>
            {
                app2.Use(next =>
                {
                    return async c =>
                    {
                        await c.Response.WriteAsync("ph1" + "\r\n");
                        await next.Invoke(c);
                    };
                });
            });
            app1.Map("/ph2", app3 =>
            {
                app3.Use(next =>
                {
                    return async c =>
                    {
                        await c.Response.WriteAsync("ph2" + "\r\n");
                        await next.Invoke(c);
                    };
                });
            });
        });
        Action<IApplicationBuilder> configuration = appr => {
            appr.Use(next =>
            {
                return async c =>
                {
                    await c.Response.WriteAsync("bc" + "\r\n");
                    await next.Invoke(c);
                };
            });
        }; 
        app.MapWhen(context =>
        {
            return context.Request.Query.ContainsKey("bc");
        }, configuration);
        
    }