Comment 1 for bug 1748712

Digging in there is an old record for what must be an old node:

maasdb=> select * from maasserver_event where node_id=16;
  id | created | updated | action | description | node_id | type_id
-------+-------------------------------+-------------------------------+--------+--------------------------+---------+---------
 96387 | 2016-07-01 17:03:36.883757+01 | 2016-07-01 17:03:36.883757+01 | | Power state queried: off | 16 | 6
(1 row)

I will try deleting that record and proceeding from there, but we should nonetheless have an upgrade strategy to deal with loose ends in the event table.