I noticed an error in my testing code where some events had no performer information in the data. It appears that the common thread is Flow (StructuredDiscussions) edits. These events don't appear to carry any other data about who made the edit triggering the event in lieu of performer.
None of our use cases are likely to be strongly impacted by this, and perhaps this is unavoidable with the way that Flow is set up, but making sure this is noted.
Here's an example:
{'added_links': [{'external': False, 'link': '/wiki/Wikip%25C3%25A9dia:Citez_vos_sources'}], 'database': 'frwiki', 'meta': {'domain': 'fr.wikipedia.org', 'dt': '2019-02-21T15:07:39+00:00', 'id': '6daa3566-35ea-11e9-9465-141877614a33', 'request_id': 'cc6416ca-cca5-4264-8eba-d995a2f75a7c', 'schema_uri': 'mediawiki/page/links-change/1', 'topic': 'eqiad.mediawiki.page-links-change', 'uri': 'https://fr.wikipedia.org/wiki/Sujet:Uumkuv2oxfcp7740', 'partition': 0, 'offset': 8066818}, 'page_id': 12391241, 'page_is_redirect': False, 'page_namespace': 2600, 'page_title': 'Sujet:Uumkuv2oxfcp7740', 'rev_id': 156928812}
For comparison, here's an event with performer:
{"added_links":[{"external":false,"link":"/wiki/Shirou_Emiya"},{"external":false,"link":"/wiki/Steep_(video_game)"},{"external":false,"link":"/wiki/Talk:Steep_(video_game)/GA1"},{"external":false,"link":"/wiki/Wikipedia:Peer_review/Shirou_Emiya/archive1"}],"database":"enwiki","meta":{"domain":"en.wikipedia.org","dt":"2019-02-21T16:40:24+00:00","id":"62a9cc32-35f7-11e9-b0e4-1866da993d2e","request_id":"XG64vwpAEDYAACGE8lYAAAAJ","schema_uri":"mediawiki/page/links-change/1","topic":"eqiad.mediawiki.page-links-change","uri":"https://en.wikipedia.org/wiki/Talk:GeForce_4_series","partition":0,"offset":8125769},"page_id":2449960,"page_is_redirect":false,"page_namespace":1,"page_title":"Talk:GeForce_4_series","performer":{"user_edit_count":15232,"user_groups":["autoreviewer","extendedconfirmed","reviewer","rollbacker","*","user","autoconfirmed"],"user_id":863426,"user_is_bot":false,"user_registration_dt":"2006-01-31T13:32:53Z","user_text":"UKER"},"rev_id":607168103}