C# 8 Book Class

Book.cs

class Book
{
  public string Title { get; }
  public string Publisher { get; }
  public string? Isbn { get; }
  public Book(string title, string publisher, string? isbn)
    => (Title, Publisher, Isbn) = (title, publisher, isbn);

  public Book(string title, string publisher)
    : this(title, publisher, null) { }

  public void Deconstruct(out string title, out string publisher, out string? isbn)
    => (title, publisher, isbn) = (Title, Publisher, Isbn);

  public override string ToString() => Title;
}

Program.cs

var book = new Book("Professional C# 8", "Wrox Press");
// string isbn = book.Isbn;  // error: converting null literal or possible null value to non-nullable type
string? isbn = book.Isbn;