How to use session variable to retrive row that contain null value

[LamKhoa]

Hi All,
I have a simple problem that has made me pondering for days on Google and still have no answer:
For example, I have following SQL query:

SELECT 
    ID, AccountNum, Name 
FROM
    Table1
WHERE
     AccountNum = @AccountNum
     Name = @Name

(In which @AccountNum and @Name are session variable).

Then in the C# code behind. I wrote:
Session["AccountNum"] = DBNull.Value;
Session["Name"] = DBNull.Value;

Logically, It would return for me a list of row in which both AccountNum and Name are NULL value. However, it didn't work. It's only work if both Name and AccountNum are varchar datatype in database (But in this case, AccountNum is a Int32 datatype).

Please let me know if any of you know any work around.

Thanks All

Lamk.