SQL Table Variable to take correct path if value in column 1 is 0 or Null

Question

I need to make changes to database in bulk from information provided on a spreadsheet.

At the moment the Table Variable values are added manually, but the hope is to do this automatically from an existing Excel front end (It's a Legacy Application that isn't worth completely re-developing)

I've created the script so that Amendments to a table in SQL can be done in one Execute, the problem I ave is checking where the code should insert a new record to the database.

With amendments there is an Old Ref which is updated to a New Ref, so all columns of the Table variable contain values.

With New records there is only a New Ref so the Old Ref will be Blank, 0 or Null (whichever it needs to be for the code.)

Here is what I have so far: (I've substituted in a 'Print' for each branch rather than showing the rest of the code which is quite long.

 @T_VAR TABLE (
 OldRef int,
 NewRef int,
 Name varchar(255),
 CustGp varchar(55),
 DelGp varchar(55),
 )

 ---BULK INSERT VALUES TO TABLE VARIABLE---
 INSERT INTO @T_VAR (
 OldRef,
 NewRef,
 Name,
 CustGp,
 DelGp
 )
 Values 
 --------//**ENTER VALUES HERE**//--------
 (1001,2010,'TestUpdate01','Group 1','Delivery 1'),
 (NULL,2012,'TestUpdate02','Group 2','Delivery 1'),
 (1547,2018,'TestUpdate03','Group 1','Delivery 3'),
 (NULL,2022,'TestUpdate04','Group 3','Delivery 1'),
 (1752,2050,'TestUpdate05','Group 1','Delivery 2')


 -----CHECK IF VARIABLE OldREF IS 0/NULL (Is this a New Record or an Amendment?)----

 IF (Select OldRef from @T_VAR) IS NULL

 Print 'Follow script to Insert New Record'

 else

 print 'Follow script to Amend Existing Record'

When running this I get the following error:

Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.

The code needs to go through each row and then divert it down the correct path- If this is possible.

I know the rest of the code works for just amendments as it's been tested.

Any help that can be given in resolving this would be very much appreciated.