While examinating [[https://it.wikinews.org/wiki/Speciale:FiltroAntiAbusi/examine/log/5048|this AbuseLog entry]] on itwikinews, the page_namespace variable has the incorrect value of null. However, in the fields below it's clearly shown as 0, and the edit was on a ns0 page, too. Trying to reproduce this error on other AbuseLog entries didn't work, and the namespace has the correct value (0 or anything else).
The first suspect could be that this is due to the edit not being saved, however other non-saved edits do have the correct value for page_namespace.
The second could be that page_namespace isn't used in any filter, and thus computed non-lazily upon examination (something similar to T176291), but the variable was actually computed at edit time.
While further investigation is coming, I have no clues for the moment.
UPDATE 1: This comes from wmf.19. In fact, page_namespace is identical to null for entries older than August 30th, 19:47 UTC, which is the deployment time.