using System;

using AutoMapper;

​

public sealed record A {

    public bool IsActive { get; init; }

}

​

public sealed record UpdateA {

    public bool? IsActive { get; init; }

}

​

public class Program

{   

    public static void Main()

    {

        var config = new MapperConfiguration(cfg => 

            {

                cfg.CreateMap<UpdateA, A>()

                    .ForAllMembers(opts => opts.Condition((src, dest, srcMember) => srcMember != null));

            });

        var mapper = config.CreateMapper();

        var a = new A { IsActive = true };

        var updateA = new UpdateA { IsActive = null };

        Console.WriteLine(a.IsActive);

        mapper.Map(updateA, a);

        Console.WriteLine(a.IsActive);

    }

}