how interactions are defined?

We have users and deals that they are booked. So if booking considered as interaction, then how could we build the interactions? In some cases, deal are not booked by anyone, and in some cases, a user didn't book any deal. So the data look like as bellow `guest_item_ids`:

| booking_id | deal_id|
|--------------|-------- |
| 100 | 200 |
| 100 | 201 |
| 101 | NULL |
| NULL | 202 |

Then if I replace NULLs with 0, I will get error ` Item id 0.0 not in item id mapping`
`dataset.build_interactions(list(zip(guest_item_ids['booking_id'], guest_item_ids['deal_id'])))`

The only entry point named is dataset.build_interactions(...); start by reading its documentation and implementation, then compare the accepted item-ID mapping with the guest_item_ids table, including NULL rows. Done would require a project decision or documentation explaining how unbooked users and deals should be represented; the issue does not name a file or test.

Written by the indexing model from the issue text.