CustomResolver.cs

public static void Main()
{
   var config = new MapperConfiguration(c =>
	{
		c.CreateMap<Model, Dto>().ForMember(d=>d.Country, o=>o.ResolveUsing<ResolveEntityFromId<Country>, long?>(s => 0));
	});
   config.AssertConfigurationIsValid();
   var mapper = config.CreateMapper();

   var source = new Model { FooId = Guid.NewGuid(), ShortDescription = "Yoyodyne Foo", FullDescription = "Deluxe Foo Manufactured by Yoyodyne, Inc.", Date = DateTime.Now.ToUniversalTime()};
   
   mapper.Map<Dto>(source);
}

public class Model
{
    public Guid FooId { get; set; }
    public string FullDescription { get; set; }
    public string ShortDescription { get; set; }
	public DateTime Date { get; set; }
}

public class Dto
{
    public Guid FooId { get; set; }
    public string FullDescription { get; set; }
    public string ShortDescription { get; set; }
	public DateTime Date { get; set; }
	public Country Country { get; set; }
}

public class Country
{
	private int _value;
	
	public int Value
	{
		get
		{
			Console.WriteLine("Get value");
			return _value;
		}
		set
		{
			_value = value; 
		}
	}
}

public class ResolveEntityFromId<T> : IValueResolver<long?, T> where T : new()
{
   public T Resolve(long? id, ResolutionContext context)
   {
       return new T();
   }
}