public class SendOrderHandler : BaseSendOrderHandler<OrderRequest, OrderResponse>
{

    ...

    protected override AxComEdiJournal BuildEdiJournal(OrderRequest order)
    {
        this.Order = order;

        var customer = order.Customer;

        if (customer == null) throw new ArgumentNullException("SendOrder has no customer defined to match a customer in AX.");

        // Get AX Customer
        var axCustomer =
            _customerService.GetCustomer(
                _mapper.Map<Customer, AxCustComSetup>(customer)
            );

        // Vendor
        var vendor = new AxVendor() { AccountNum = "111", Name = "VENDOR" };

        // Get AX Articles
        var articles = _mapper.Map<IEnumerable<OrderLine>, IEnumerable<AxComArticle>>(order.Order.OrderLines);
        articles = _articleService.GetArticles(
            _mapper.Map(vendor, articles).ToList()
        );

        // Create EDI Journal and return true if succeeded
        var ediJournal = _mapper.Map<AxCustomer, AxComEdiJournal>(axCustomer);
        _mapper.Map(vendor, ediJournal);
        _mapper.Map(order.Order, ediJournal);

        var ediJournalLines = _mapper.Map<IEnumerable<AxComArticle>,
            IEnumerable<AxComEdiJournalLine>>(articles);
        ediJournal.Lines = ediJournalLines.ToList();
        ediJournal.CreateDate = DateTime.Now;
        ediJournal.OrderId = string.Empty;
        ediJournal.Remark = string.Empty;

        return ediJournal;
    }
}

public class SendOrderHandler : BaseSendOrderHandler<MultiShipmentOrder, OrderResponse>
{

    ...

    protected override AxComEdiJournal BuildEdiJournal(MultiShipmentOrder order)
    {
        var user = order.OrderPartyInformation?.User;

        if (user == null) throw new ArgumentNullException("MultiShipmentorder has no user defined to match a customer in AX.");

        // Get AX Customer
        var customer =
            _customerService.GetCustomer(
                _mapper.Map<User, AxCustComSetup>(user)
            );

        // Vendor
        var vendor = new AxVendor() { AccountNum = "2222", Name = "VENDOR2" };

        // Get AX Articles
        var articles = _mapper.Map<IEnumerable<MultiShipmentOrderLineItem>, IEnumerable<AxComArticle>>(order.MultiShipmentOrderLineItems);
        articles = _articleService.GetArticles(
            _mapper.Map(vendor, articles).ToList()
        );

        // Create EDI Journal and return true if succeeded
        var ediJournal = _mapper.Map<AxCustomer, AxComEdiJournal>(customer);
        _mapper.Map(vendor, ediJournal);
        _mapper.Map(order, ediJournal);
        var ediJournalLines = _mapper.Map<IEnumerable<AxComArticle>, IEnumerable<AxComEdiJournalLine>>(articles);
        ediJournal.Lines = ediJournalLines.ToList();
        ediJournal.CreateDate = DateTime.Now;
        ediJournal.OrderId = string.Empty;
        ediJournal.Remark = string.Empty;

        return ediJournal;
    }
}

public abstract class BaseSendOrderHandler<TIn, TOut> : BaseHandler<TOut>, ISendOrderHandler<TIn, TOut>
    where TIn : class where TOut : class
{
    protected AxComEdiJournal EdiJournal { get; private set; }

    ...

    public void Process(TIn order)
    {
        this.IsValid = false;

        // Build Edi Journal
        this.EdiJournal = BuildEdiJournal(order);

        // Validate
        ...
    }

    protected abstract AxComEdiJournal BuildEdiJournal(TIn order);
}