Enotice on participant delete

I hit this on 4.7 – not sure if it exists on 4.6 too but that seems likely to me as I believe the change that triggered it may have been in around 4.6.3.

Steps -

• from an event choose the link to view participants.
• Choose all & the delete action.
• After confirm when the page reloads:

Warning: array_key_exists(): The first argument should be either a string or an integer in array_key_exists() (line 55 of /home/vagrant/civicrm-buildkit/build/drupal-demo/sites/all/modules/civicrm/CRM/Utils/Array.php). =>

23: array_key_exists() (Array, 1 element)
22: CRM_Utils_Array::value() (Array, 2 elements)
21: CRM_Contact_BAO_Query::buildQillForFieldValue() (Array, 2 elements)
20: CRM_Event_BAO_Query::whereClauseSingle() (Array, 2 elements)
19: CRM_Event_BAO_Query::where() (Array, 2 elements)
18: CRM_Core_Component::alterQuery() (Array, 2 elements)
17: CRM_Contact_BAO_Query->whereClause() (Array, 2 elements)
16: CRM_Contact_BAO_Query->initialize() (Array, 2 elements)
15: CRM_Contact_BAO_Query->__construct() (Array, 2 elements)
14: CRM_Event_Selector_Search->__construct() (Array, 2 elements)