Self-generating code is not a good thing. Non-ecsaped string data will cause you pain and maintaining the code will be terrible.

SELECT * FROM Production.Product

WHERE

(@ProductNumber IS NULL OR...

What if you would like to query using a where clause?

For example...

SELECT COUNT(*) FROM books WHERE title LIKE '%Harry Potter%'

Or...

SELECT COUNT(*) FROM invoices WHERE deleted = 0

I could be wrong...