Why not pass in XML into the SP? I.e.

@BrandId_List XML --e.g. <Brands><id>1</id><id>2</id></Brands>

And then your query could look like this:

SELECT *

FROM

Sales s

INNER JOINProducts p on s.customerId = p.customerId

INNER JOINBrands b on p.BrandId = b.BrandId

WHERE

tb.BrandId IN (SELECT Brands.ID.value('.','INT')

FROM @BrandId_List.nodes('/Brands/id') AS Brands(ID))

OR @BrandID_List IS NULL

By passing NULL for the parameter would still achieve the same result; you would just have to build the XML before passing into the SP. Also worth noting that you can apply an XML namespace here to make sure your XML markup conforms to a set standard.