Remove nulls from TSQL connection string
SQL Server always returns NULLs in this case. I know of no way to globally (through server settings or connection strings) cause it to return empty strings or zeroes instead of NULLs. And I do not think it is a database library issue--using different drivers won't change a thing. This is just the way SQL Server behaves.

If you want to convert NULLs to something else, you'll need to explicitly use the IsNull(Expression, ValueIfNull) function or the similar Coalesce() function which takes multiple parameters and returns the first non-null value.

SELECT O.OrderID, IsNull(CustomerName, '') CustomerName
FROM
   dbo.OrderTable O
   LEFT JOIN dbo.CustomerTable C
      ON O.OrderCustomerID = C.CustomerID


Though one comment... why would there be an order with no customer? Wouldn't a customer with no order be more likely?

Update

Can you put in a wrapper that, client side, converts the NULLs to what you want? What process or program are you using to convert the result sets to text?