I have a client that is having issues with a portion of users sending (not set) as the value for their first pageview (landing page). I suspect a problem with the Tag Management Software configuration, but I can't be sure beacuse I have not been able to query this in BigQuery. 

I don't see values for any of the following WHERE clauses: `hits.page.pagePath IS NULL`, `hits.page.pagePath = '(not set)'`, or `hits.page.pagePath = ''`

I feel like I'm missing something obvious here...