public void SetCoverImage(Book book, string imagePath)
 {
     if (book == null)
     {
         throw new ArgumentNullException("Book cannot be null.");
     }
     var imageToUpdate = book.Images.Where(i => i.ImagePath == imagePath).FirstOrDefault();
     if (imageToUpdate != null)
     {
         imageToUpdate.IsCoverImage = true;
     }
 }
 public void DisplayBook(Book book, StringBuilder sb)
 {
     if (book == null)
     {
         throw new ArgumentNullException("Book cannot be null.");
     }
     sb.AppendLine(book.Title);
     var coverImage = book.Images.Where(i => i.IsCoverImage).FirstOrDefault();
     if (coverImage != null)
     {
         sb.AppendLine("Cover Image: " + coverImage.ImagePath);
     }
     foreach (var image in book.Images)
     {
         sb.AppendLine(image.ImagePath);
     }
 }