Why does .ToString() on a null string cause a null error, when .ToString() works fine on a nullable int with null value?

Question

selectedItem has two fields:

• int? _cost
• string _serialNumber

In this example, _cost

Answer 1

A string is a reference type, but a nullable int is a value type. Here is a Good discussion of the differences http://www.albahari.com/valuevsreftypes.aspx.