TrelloUser.cs

public class TrelloUser
{
    public string Id { get; set; }
    public string AvatarUrl { get; set; }
    public string FullName { get; set; }
    public string Initials { get; set; }

    public IEnumerable<TrelloBoard> Boards { get; set; }

    public IEnumerable<TrelloOrganization> Organizations { get; set; }

    public string GetAvatar(int size)
    {
        return $"{AvatarUrl}/{size}.png";
    }

    public IEnumerable<TrelloBoard> GetBoardsByOrganization(string idOrganization)
    {
        return Boards.Where(x => x.IdOrganization == idOrganization);
    }
}