efq_views_handler_argument_property_string::query() incompatible with views_handler_argument_string

There's a parameter missing from the method declaration:

Strict warning: Declaration of efq_views_handler_argument_property_string::query() should be compatible with views_handler_argument_string::query($group_by = false) in require_once() (line 6 of /path/to/drupal/sites/all/modules/contrib/efq_views/handlers/efq_views_handler_argument_property_string.inc).