Solving this one:
2021-10-28 17:56:31,879,879ms [PID: 2982487] workers.github_worker.57714 [DEBUG] Enriching 11572 contributors.
2021-10-28 17:56:31,879,879ms [PID: 2982487] workers.github_worker.57714 [INFO] nan not in database, making api call
2021-10-28 17:56:31,879,879ms [PID: 2982487] workers.github_worker.57714 [INFO] login: nan
2021-10-28 17:56:31,879,879ms [PID: 2982487] workers.github_worker.57714 [INFO] Error when creating url: can only concatenate str (not "float") to str. Data: {'id': 2046382478, 'issue_id': 36162, 'node_id': 'MDE0Ok1lbnRpb25lZEV2ZW50MjA0NjM4MjQ3OA==', 'url': 'https://api.github.com/repos/chaoss/augur/issues/events/2046382478', 'actor': {}, 'created_at': Timestamp('2018-12-27 20:09:55'), 'event': 'mentioned', 'commit_id': None, 'actor.login': nan, 'actor.id': nan, 'actor.node_id': nan, 'actor.avatar_url': nan, 'actor.gravatar_id': nan, 'actor.url': nan, 'actor.html_url': nan, 'actor.followers_url': nan, 'actor.following_url': nan, 'actor.gists_url': nan, 'actor.starred_url': nan, 'actor.subscriptions_url': nan, 'actor.organizations_url': nan, 'actor.repos_url': nan, 'actor.events_url': nan, 'actor.received_events_url': nan, 'actor.type': nan, 'actor.site_admin': nan}

…Hub user NaN, who is interpreted as a float.