Insert foreign key with and without Null value

I have a relational database in MS Access which contains 4 tables: dummyTable, Table1, Table2, Table3. dummyTable holds the foreign keys of others.

Now, for inserting, I am using the query:

INSERT INTO dummyTable (Col1, Col2, Col3, FK_Table1ID, FK_Table2ID, FK_Table3ID)
    SELECT '25' AS Expr1, 'test2' AS Expr2, 2 AS Exp3, Table1.ID, Table2.ID, Table3.ID
    FROM Table1, Table2, Table3
    WHERE (((Table1.dummyName) = 'Germany') 
            AND ((Table2.dummyName) = 'Berlin') 
            AND ((Table3.dummyName) = 'dummyStreet'));

Which is basically, selecting other columns value and insert the foreign keys in my main table (dummyTable). This is working.

But the problem is here some of the values are optional. Let's say I must not have Table2.dummyName. If I try ((Table2.dummyName)='') Or ((Table2.dummyName)=Null). It doesn't insert anything / 0 row inserted in precise but runs successfully.

My query actually connected with VB.Net at the backend so I want to send DBNull.Value in my parameter. I have tried also only the selecting query:

SELECT '25' AS Expr1, 'test2' AS Expr2, 2 AS Exp3, Table1.ID, Table2.ID, Table3.ID, Table4.ID
FROM Table1, Table2, Table3
WHERE (((Table1.dummyName)='Germany') AND ((Table2.dummyName)=Null) AND ((Table3.dummyName)='dummyStreet'));

And it produces no rows. So I tried:

.....(upper part is the same)
WHERE (((Table1.dummyName)='Germany') AND (IIF(((Table2.dummyName)=Null), Table2.ID = Null, ((Table2.dummyName)='Berlin')) AND ((Table3.dummyName)='dummyStreet'));

But again, no row inserted in case of Null, but works When (IIF(((Table2.dummyName)='Berlin'), Table2.ID = Null, ((Table2.dummyName)='Berlin'))

Can anyone please help me with it? I am really stuck here. Is it possible by using IIF or Switch, or I am completely in the wrong direction?

Solution

Well, it turns out you can. Whether it's best or not. The code:

INSERT INTO dummyTable (Col1, Col2, Col3, FK_Table1ID, FK_Table2ID, FK_Table3ID)
    SELECT Top 1 '25' AS Expr1, 'test2' AS Expr2, 2 AS Exp3, 
      IIf(((Select t1.ID From Table1 t1 Where Exists (SELECT t1.ID FROM Table1 t1 WHERE 
       t1.dummyName = 'Germany') AND t1.dummyName = 'Germany') Is Null),t1.ID=Null,(Select 
       t1.ID From Table1 t1 Where t1.dummyName = 'Germany')) AS TableOne,
      IIf(((Select t2.ID From Table2 t2 Where Exists (SELECT t2.ID FROM Table2 t2 WHERE 
       t2.dummyName = 'Berlin') AND t2.dummyName = 'Berlin') Is Null),t2.ID=Null,(Select 
       t2.ID From Table2 t2 Where t2.dummyName = 'Berlin')) AS TableTwo,
      IIf(((Select t3.ID From Table3 t3 Where Exists (SELECT t3.ID FROM Table3 t3 WHERE 
       t3.dummyName = 'dummyStreet') AND t3.dummyName = 'dummyStreet') Is 
       Null),t3.ID=Null,(Select t3.ID From Table3 t3 Where t3.dummyName = 'dummyStreet')) 
       AS TableThree
    FROM Table1 As t1, Table2 As t2, Table3 As t3;

Please keep in mind this is just a dummy Code so I didn't put afford to go with parameters. It's highly recommended not to do so.