C# nullable string error

Solution 1:

System.String is a reference type and already "nullable".

Nullable<T> and the ? suffix are for value types such as Int32, Double, DateTime, etc.

Solution 2:

You are making it complicated. string is already nullable. You don't need to make it more nullable. Take out the ? on the property type.

Solution 3:

string cannot be the parameter to Nullable because string is not a value type. String is a reference type.

string s = null; 

is a very valid statement and there is not need to make it nullable.

private string typeOfContract
    {
      get { return ViewState["typeOfContract"] as string; }
      set { ViewState["typeOfContract"] = value; }
    }

should work because of the as keyword.