event_id not required in schema

I just noticed that the field civicrm_participant.event_id is not identified as 'required' in the CRM_Event_DAO_Participant->fields() function & the mysql field is not set to 'not null'. These 2 are because the xml that defines the field does not have 'required' ie.

<required>true</required>

I presume that the the upgrade script would also require tweaking somewhere