ASP.NET Automapper add to list of objects in map profile

To create PersonalChatDto

1. I first create dto and map Chat class into it
2. Map member options to existing dto
3. Map partner(user I talk to) to existing dto
4. And if partner is in contact book, i want mapper to take value of List<AvatarDto> Avatars and add avatar from contact to it.

var partner = chat.Members.Single(u => u.Id != user.Id);

        var contact = await contactRepository.GetContactAsync(user.Id, partner.Id);

        var member = await personalChatMemberRepository.GetMemberAsync(chat.Id, user.Id);

        var dto = mapper.Map<PersonalChatDto>(chat);
        mapper.Map(member, dto);
        mapper.Map(partner, dto);
        mapper.Map(contact, dto);

        return Result<PersonalChatDto>.Success(dto);

The problem is in mapping profile it shows me

var avatars = destMember ?? [];
var contactAvatar = src.CustomAvatar;

All props have correct values and even returns correct values.

1. avatars value
2. contactAvatar value
3. return value

But after all mappings dto’s Avatars field is empty list

1. dto object after all maps
2. result

Here is mapping profile

CreateMap<Contact, PersonalChatDto>()
            .ForMember(dest => dest.Id,
                opt => opt.Ignore())
            .ForMember(dest => dest.FirstName, opt =>
                opt.MapFrom(src => src.CustomFirstName))
            .ForMember(dest => dest.LastName, opt =>
                opt.MapFrom(src => src.CustomLastName))
            .ForMember(dest => dest.Avatars, opt =>
                opt.MapFrom((src, _, destMember, context) =>
                {
                    var avatars = destMember ?? [];
                    var contactAvatar = src.CustomAvatar;

                    if (contactAvatar is null) return avatars;
                    
                    avatars.Add(context.Mapper.Map<AvatarDto>(contactAvatar));
                    
                    return avatars;
                }));

Contact class

public sealed class Contact : IEntity<Guid>
{
    public Guid OwnerId { get; set; }

    public User Owner { get; set; }

    public Guid UserId { get; set; }

    public User User { get; set; }

    public string CustomFirstName { get; set; }

    public string? CustomLastName { get; set; }

    public Guid CustomAvatarId { get; set; }

    public ContactAvatar? CustomAvatar { get; set; }

    public Guid Id { get; set; } = Guid.NewGuid();
}

PersonalChatDto record

public sealed record PersonalChatDto(
    [Required] Guid Id,
    [Required] string UserName,
    [Required] string FirstName,
    string? LastName,
    string? Biography,
    List<AvatarDto>? Avatars,
    [Required] bool IsMuted)
{
    public PersonalChatDto() 
        : this(default, default!, default!, null, null, null, default)
    {
    }
};

I was trying to configure map profile to add to list of existing items, instead of setting new value.