C# automapper nested collections

I have a simple model like this one:

public class Order{
   public int Id { get; set; }
   ... ...
   public IList<OrderLine> OrderLines { get; set; }
}

public class OrderLine{
   public int Id { get; set; }
   public Order ParentOrder { get; set; }
   ... ...
}

What I do with Automapper is this:

    Mapper.CreateMap<Order, OrderDto>();
    Mapper.CreateMap<OrderLine, OrderLineDto>();
    Mapper.AssertConfigurationIsValid();

It throw an exception that says: "The property OrderLineDtos in OrderDto is not mapped, add custom mapping ..." As we use a custom syntax in our Domain and in our DomainDto, how I can specify that the collection OrderLineDtos in OrderDto corresponds to OrderLines in Order?

Thank you