Undefined index: entity keys in entity_extract_ids()

Environment:

 Package           Name                                           Version
 Chaos tool suite  Chaos tools (ctools)                           7.x-1.3
 Fields            Entity Reference (entityreference)             7.x-1.1
 Organic groups    Organic groups (og)                            7.x-2.4
 Organic groups    Organic groups UI (og_ui)                      7.x-2.4
 Other             Entity API (entity)                            7.x-1.2
 Views             Views (views)                                  7.x-3.7
 Views             Views Bulk Operations (views_bulk_operations)  7.x-3.1

Message:

Notice: Undefined index: entity keys in entity_extract_ids() (line 7691 of /var/aegir/platforms/d201312161012/includes/common.inc).
Notice: Undefined index: entity keys in entity_extract_ids() (line 7692 of /var/aegir/platforms/d201312161012/includes/common.inc).

Steps to reproduce:

1. Create a fresh og installation with Standard D7 profile
2. Make the basic page content type Group Content
3. Edit og_group_ref
4. Save field (no changes necessary)

The problem seems to be the validate function that was expanded in OG 7.x-2.4, specifically the following line:

list(,, $bundle) = entity_extract_ids($entity_type, $entity);

However, $entity_type and $entity are both null. The $bundle variable is not actually used in the validate function so maybe the call to entity_extract_ids can be removed or, if a value for $bundle is required, it can be retrieved from the $instance array.