Object reference not set to an instance of an object

With C# .Net, many times you may need to typecast an object value to string. And you might have noticed that it throws null reference exception as ”Object reference not set to an instance of an object”. This is a run time exception & will occur mostly when you try to typecast a null value to string.

For example:
String userId = Session[“user”].ToString();

Above code will run fine until Session[“user”] have some value but throw exception when it has null value. You can sort out these problem by casting it through Convert.ToString().

For example:
String userId = Convert.ToString(Session[“user”]);

Now your code will not throw any such exception even when it has null value and will cast null value to empty string.

:)