Hi!

I'm trying to upgrade a site from CMS 11 to 12 and the site compiles but wont startup.

public class Program
{
    public static void Main(string[] args)
    {
        var environment = Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT");
        var isDevelopment = environment == Environments.Development;

        if (isDevelopment)
        {
            Log.Logger = new LoggerConfiguration()
                .MinimumLevel.Warning()
                .WriteTo.File("app_data/log.txt", rollingInterval: RollingInterval.Day)
                .CreateLogger();
        }


        CreateHostBuilder(args, isDevelopment).Build().Run();
    }

    public static IHostBuilder CreateHostBuilder(string[] args, bool isDevelopment)
    {
        if (isDevelopment)
        {
            return Host.CreateDefaultBuilder(args)
                .ConfigureAppConfiguration(config =>
                {
                    config.AddJsonFile($"appsettings.{Environment.GetEnvironmentVariable("COMPUTERNAME")}.json", optional: true, reloadOnChange: true);
                })
                .ConfigureCmsDefaults()
                .UseSerilog()
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                });
        }
        else
        {
            return Host.CreateDefaultBuilder(args)
                .ConfigureCmsDefaults()
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                });
        }
    }
}

public class Startup
{
    private readonly IWebHostEnvironment _webHostingEnvironment;
    private readonly IConfiguration _configuration;

    
    public Startup(IConfiguration configuration, IWebHostEnvironment webHostEnvironment)
    {
        _configuration = configuration;
        _webHostingEnvironment = webHostEnvironment;
    }


    // This method gets called by the runtime. Use this method to add services to the container.
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddMvc()
            .AddRazorOptions(ro => ro.ViewLocationExpanders.Add(new FeatureViewLocationExpander()));

        if (_webHostingEnvironment.IsDevelopment())
        {
            services.Configure<ClientResourceOptions>(uiOptions =>
            {
                uiOptions.Debug = true;
            });
        }

        services.AddEmbeddedLocalization<Startup>();
    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }

        app.UseStaticFiles();
        app.UseRouting();
        app.UseAuthentication();
        app.UseAuthorization();
        
        app.UseEndpoints(endpoints =>
        {
            endpoints.MapControllerRoute(name: "Default", pattern: "{controller}/{action}/{id?}");
            endpoints.MapControllers();
            endpoints.MapContent();
        });

    }
}

gives me: 

InvalidOperationException: Sequence contains no matching element
System.Linq.ThrowHelper.ThrowNoMatchException()
System.Linq.Enumerable.First<TSource>(IEnumerable<TSource> source, Func<TSource, bool> predicate)
EPiServer.DependencyInjection.ServiceLocatorProviderFactoryFacade<TContainerBuilder>.CreateBuilder(IServiceCollection services)
Microsoft.Extensions.Hosting.Internal.ServiceFactoryAdapter<TContainerBuilder>.CreateBuilder(IServiceCollection services)
Microsoft.Extensions.Hosting.HostBuilder.CreateServiceProvider()
Microsoft.Extensions.Hosting.HostBuilder.Build()
Web.Episerver12.Program.Main(string[] args) in Program.cs
+
            CreateHostBuilder(args, false).Build().Run();

I guess it could be the Core projects setup as well but I cannot figure this one out.

Thanks!

/Kristoffer