If you use the RFI-lookup-and-save-user playbook to Lookup leaks info for an email and response lookup data is empty (for specified email and look back range) - the playbook will still save empty results to the Log Analytics Custom Log.
This case is possible if you set up the Playbooks in that way that Lookup look back range (lookup_lookback_days) in RFI-lookup-and-save-user playbook is smaller than Search look back range (search_lookback_days) in RFI-search-workforce-user or RFI-search-external-user playbooks.
In that case you will see some empty records in the corresponding Log Analytics Custom Log (see the screenshot).
Another way to cover this case - you can add a corresponding check to RFI-lookup-and-save-user playbook and not save the results to Log Analytics if the result is empty.