using System;

using AutoMapper;

public class Program

{

    public static void Main()

    {

        var config = new MapperConfiguration(cfg => cfg.CreateMap<Book, Book>()

                                             .ForAllMembers(opts => opts.Condition((src, dest, member) => member != null || member != default)));

        var mapper = config.CreateMapper();

        var target = new Book

        {

            Author = "1",

            Title = "1",

            EAN = "1",

            Id = Guid.NewGuid()

        };

​

        var source = new Book

        {

            Author = "",

            Title = "2",

        };

        var book = mapper.Map(source, target);

        Console.WriteLine(book.Author + "-" + book.Title + "-" + book.EAN + " - " + book.Id);

    }

    public class Book{

        public string? Author {get; set;}

        public string? Title {get; set;}

        public string? EAN {get; set;}

        public Guid Id {get; set;}

    }

}