I came up with my solution and then checked it against the provided solution. The provided solution makes no sense to me. It looks like the solution starts reporting pairs where one store is null whenever there are less than five stores. In a real-life situation, I would assume that we either had an error in the solution or a unique use case. Since it would be easy to add a bunch of store pairs including nulls later I just solved for unique unordered pairs. Did it a little differently than most, generating all the combinations numerically and then adding store names.