Can someone pls explain why this is happening. I’m trying to get Orders from in memory database but Customer is always null

private async Task<IList<RepositoryOrder>> GetOrdersInternalAsync(int skip, int count)
    {
        var repositoryOrders = await this.context.Orders
            .Include(x => x.Customer)
            .Include(x => x.Employee)
            .Include(x => x.Shipper)
            .Include(x => x.OrderDetails).ThenInclude(x => x.Product)
            .Skip(skip)
            .Take(count)
            .OrderBy(x => x.Id)
            .Select(x => OrderMapper.Map(x))
            .ToListAsync();

        return repositoryOrders;
    }

This is Order model:

public class Order
{

    public Order(long id, Customer customer, // other properties)
    {
    }

    private Order()
    {
    }

    public long Id { get; }

    public virtual Customer Customer { get; set; } = null!;
    
    // other properties

}

And this is Customer model:

public class Customer
{
    public Customer(CustomerCode code, string companyName)
    {
        this.CustomerCode = code;
        this.CompanyName = companyName;
    }

    private Customer()
    {
    }

    public CustomerCode CustomerCode { get; }

    public string CompanyName { get; }
}
public class CustomerCode
{
    public CustomerCode(string code)
    {
        this.Code = code;
    }

    public string Code { get; init; }
}

This is how i configured relationship:

modelBuilder.Entity<Customer>(opt =>
        {
            opt.ToTable("Customers");
            opt.Property(x => x.CustomerCode)
                .HasConversion(x => x.Code, y => new CustomerCode(y))
                .HasColumnName("CustomerID")
                .IsRequired();
            opt.HasKey(x => x.CustomerCode);
            opt.Property(x => x.CompanyName).HasMaxLength(255);
        });
    modelBuilder.Entity<Order>(opt =>
        {
            opt.ToTable("Orders");
            opt.HasKey(x => x.Id).HasName("OrderID");
            opt.Property(x => x.Id).HasColumnName("OrderID");
            opt.HasOne(x => x.Customer).WithMany().HasForeignKey("CustomerID");
    // other unrelated properties

It seems it correctly queries and selects c.CustomerID (which is CustomerCode in my code) and c.CompanyName but fails to map it:

public static RepositoryOrder Map(Order order)
    {
        var repositoryOrder = new RepositoryOrder(order.Id)
        {
            Customer = new RepositoryCustomer(new RepositoryCustomerCode(order.Customer.CustomerCode.Code)) // this is null here and throwing exception
            {
                CompanyName = order.Customer.CompanyName,
            },

Customer must be not null and in database there is no Order that has null CustomerID