using System;

using AutoMapper;

using AutoMapper.Configuration;

​

public class Program

{

    public static void Main()

    {

        var config = new MapperConfiguration(cfg =>

        {

            cfg.CreateMap<TheDto, TheModel>()

                .ForMember(dest => dest.Id, opt => opt.NullSubstitute(Guid.Empty))// .ForMember(dest => dest.Internal, opt => opt.NullSubstitute(""))

                .AfterMap((dto, model) => model.Internal ??= "NotNull");

        }

​

        );

        var mapper = config.CreateMapper();

        // execute

        var dto = new TheDto{Id = null, Type = Guid.NewGuid(), Title = null, Description = "any desc", };

        var model = mapper.Map<TheModel>(dto);

        model.Dump();

    }

}

​

public class TheModel

{

    public Guid? Id

    {

        get;

        set;

    }

​

    public Guid Type

    {

        get;

        set;

    }

​

    public string Title

    {

        get;

        set;

    }

​

    = null !;

    public string Description

    {

        get;

        set;

    }

​

    = null !;

    public string? ItIsAnything

    {

        get;

        set;

    }

​

    public string Internal

    {

        get;

        set;

    }

​

    = null !;

    public string? AnotherInternal

    {

        get;

        set;

    }

}

​

public class TheDto

{

    public Guid? Id

    {

        get;

        set;

    }

​

    public Guid Type

    {

        get;

        set;

    }

​

    public string? Title

    {

        get;

        set;

    } //  is nullable in the dto

​

    public string Description

    {

        get;

        set;

    }

​

    = null !;

    public string? ItIsAnything

    {

        get;

        set;

    }

}