var nrole= await _roleManager.CreateAsync(new IdentityRole("Administrator"));
            string user = "mail@mail.com";
            string password = "D#4uwuw!";
            var result = await _userManager.CreateAsync(new ApplicationUser { UserName = user, Email = user, EmailConfirmed = true }, password);

if (result.Succeeded)
{
 var user1 = await _userManager.AddToRoleAsync(await _userManager.FindByNameAsync(user), "Administrator");
}

System.NullReferenceException: 'Object reference not set to an instance of an object.