Warning asetracker_views_handler_field_case_count::pre_render($values) incompatible with views_handler_field::pre_render(&$values)

Whenever I enable casetracker I get the following warning in every page:

Warning: Declaration of casetracker_views_handler_field_case_count::pre_render($values) should be compatible with views_handler_field::pre_render(&$values) in include_once() (line 3469 of /www/drupal7/docroot/includes/bootstrap.inc).