Hi, @mlcubed Welcome to the Microsoft Q&A Platform, and thanks for your query.
I would normally try to use the ternary operator or an expression with "OR" but have not tried to test that answer out.
If you are writing that query in code, it may be easier to put evaluation of the optional parameter client-side to save on RUs anyways. If you are forced to do it in SQL query then you should check out the ternary operator.
Can you do something like this? The query will change based on your data model.
SELECT * FROM c WHERE c.region = @region AND (ARRAY_CONTAINS(c.businesses, @business) OR c.businesses = null)
Regards
Geetha