Hi Dears,

i post you this error before Here https://our.umbraco.org/forum/developing-packages/80623-object-reference-not-set-to-an-instance-of-an-object but i found the problem but i cannot solved

this code below is the reason when register dependencies

        var builder = new ContainerBuilder();
        builder.RegisterControllers(Assembly.GetExecutingAssembly());
        builder.RegisterApiControllers(typeof(UmbracoApplication).Assembly);
        builder.RegisterType<Ta2healDbContext>().As<IUnitOfWork>().InstancePerReques();
        builder.RegisterType<SubjectService>().As<ISubjectService>().InstancePerLifetimeScope();
        builder.RegisterType<SectionService>().As<ISectionService>().InstancePerLifetimeScope();
        builder.RegisterType<LessonService>().As<ILessonService>().InstancePerLifetimeScope();

        // Set the dependency resolver to be Autofac.
        var container = builder.Build();
        var resolver = new AutofacWebApiDependencyResolver(container);
        GlobalConfiguration.Configuration.DependencyResolver = resolver;
        DependencyResolver.SetResolver(new AutofacDependencyResolver(container));

and this when i stop some code of register dependencies

it's work when i do this into register dependencies code

       var builder = new ContainerBuilder();
        builder.RegisterControllers(Assembly.GetExecutingAssembly());
        builder.RegisterApiControllers(typeof(UmbracoApplication).Assembly);
        builder.RegisterType<Ta2healDbContext>().As<IUnitOfWork>().InstancePerRequest();

        builder.RegisterType<SubjectService>().As<ISubjectService>().InstancePerLifetimeScope();
        builder.RegisterType<SectionService>().As<ISectionService>().InstancePerLifetimeScope();
        builder.RegisterType<LessonService>().As<ILessonService>().InstancePerLifetimeScope();
        // Set the dependency resolver to be Autofac.
        //var container = builder.Build();
        //var resolver = new AutofacWebApiDependencyResolver(container);
        //GlobalConfiguration.Configuration.DependencyResolver = resolver;
        //DependencyResolver.SetResolver(new AutofacDependencyResolver(container));

but code that i stopped make some problem to me so i ask you if anyone have idea what can i do to solve this problem?