Null values indicate that there isn't any data in Lever that corresponds with that field.
For example: A Null value when viewing a workbook broken down by Posting Team would indicate that there are job posting(s) in Lever that have not been assigned to a team.
You can quickly identify the culprit job posting(s) by either drilling into the data within Lever Talent Intelligence or by going to the job postings page and looking at all job postings assigned to the Unspecified team.
Once you have updated the field(s), the data sources / worksheets / and dashboards within Lever Talent Intelligence will update within 24-48 hours.