An error occurred while calling method 'BuildWebHost' on class 'Program'

When I run dotnet ef migrations add Initial_Identity, I got this error:

An error occurred while calling method 'BuildWebHost' on class 'Program'. Continuing without the application service provider. Error: GenericArguments1, 'Microsoft.AspNetCore.Identity.IdentityRole', on 'Microsoft.AspNetCore.Identity.EntityFrameworkCore.UserStore`9[TUser,TRole,TContext,TKey,TUserClaim,TUserRole,TUserLogin,TUserToken,TRoleClaim]' violates the constraint of type 'TRole'. An operation was scaffolded that may result in the loss of data. Please review the migration for accuracy.

How can I solve it?

Here is my code:

Startup class:

public void ConfigureServices(IServiceCollection services)
{
    // some codes
    services.AddIdentity<User, IdentityRole>().AddEntityFrameworkStores<ApplicationDbContext>().AddDefaultTokenProviders();
}

Program class:

public class Program
{
    public static void Main(string[] args)
    {
        BuildWebHost(args).Run();
    }

    public static IWebHost BuildWebHost(string[] args) =>
        WebHost.CreateDefaultBuilder(args)
            .UseStartup<Startup>()
            .UseDefaultServiceProvider(options => options.ValidateScopes = false)
            .Build();
}

TemporaryDbContextFactory class:

public class TemporaryDbContextFactory : 
IDesignTimeDbContextFactory<ApplicationDbContext>
{
    //////// 
    public ApplicationDbContext CreateDbContext(string[] args)
    {
        var builder = new DbContextOptionsBuilder<ApplicationDbContext>();
        IConfigurationRoot configuration = new ConfigurationBuilder()
            .SetBasePath(AppDomain.CurrentDomain.BaseDirectory)
            .AddJsonFile("appsettings.json")
            .Build();

        builder.UseSqlServer(configuration.GetConnectionString("DefaultConnection"));
        return new ApplicationDbContext(builder.Options);
    }
}

ApplicationDbContext class:

public class ApplicationDbContext : IdentityDbContext<User, CustomRole, int,   CustomUserClaim, CustomUserRole, CustomUserLogin, CustomRoleClaim,   CustomUserToken>
{
    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options) : base(options)
    {

    }

// some codes
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<CustomUserLogin>().HasKey(a => new { a.UserId });
        modelBuilder.Entity<CustomUserRole>().HasKey(a => new { a.RoleId, a.UserId });
        modelBuilder.Entity<CustomUserToken>().HasKey(a => new { a.UserId});
    }

 // some codes

        modelBuilder.Entity<User>().ToTable("User");
        modelBuilder.Entity<CustomRole>().ToTable("Role");
        modelBuilder.Entity<CustomRoleClaim>().ToTable("RoleClaim");
        modelBuilder.Entity<CustomUserClaim>().ToTable("UserClaim");
        modelBuilder.Entity<CustomUserLogin>().ToTable("UserLogin");
        modelBuilder.Entity<CustomUserRole>().ToTable("UserRole");
        modelBuilder.Entity<CustomUserToken>().ToTable("UserToken");

}

Related to Identity:

public class CustomUserLogin : IdentityUserLogin<int> { }
public class CustomUserRole : IdentityUserRole<int> { }
public class CustomUserToken : IdentityUserToken<int> { }
public class CustomRole : IdentityRole<int> { }
public class CustomRoleClaim : IdentityRoleClaim<int> { }
public class CustomUserClaim : IdentityUserClaim<int> { }
public class User : IdentityUser<int> { }

UPDATE 1: The question has been updated!

According to Tao's answer, I corrected my code. Now the yellow error is solved but now there appeared a red error!

How can I solve this error?

Value cannot be null. Parameter name: connectionString

Contain of appsettings.json file:

{
  "ConnectionStrings": {
    "DefaultConnection": "Data Source='';initial catalog=Jahan-Beta;User ID=sa;password=''; Persist Security Info=True; Encrypt=False;TrustServerCertificate=False; MultipleActiveResultSets=True"
  }
}

I also copied appsettings.json in \bin\Debug\netcoreapp2.0 directory.