I know that you changed the behaviour of events from this Forthcoming Change to Web Intent Events
This event will populate the followed user_id or screen_name in the event object’s data argument, depending on the parameters you provided in the web intent."
But actually you wont be able to access neither user_id nor screen_name because of the event behaviour change. I lost some of my valuable time to understand that you changed the behaviour recently because the changes as per your announcements was not reflected in the documentation.
Kindly update the documentation also along with this kind of behavioural changes in events or core parts.