Session Null question

I have a ViewState on my page which is defined something like this:

 

private int Year

{

   get

       {

           if ((ViewState)["Year"] == null)

              (ViewState)["Year"] = -1;

          return (int)(ViewState)["Year"];

      }

   set

       {

           (ViewState)["Year"] = value;

       }

}

 

In the Master Page; 

protected void Page_Init(object sender, EventArgs e)

{

        Year = ...