Strict warning: Only variables should be passed by reference in heartbeat_block_view()

On Drupal 7.22 and PHP 5.4, the heartbeat_block_view() function trigger a strict warning.

Strict warning: Only variables should be passed by reference in heartbeat_block_view() (line 336 of /****/drupal-7.22/sites/all/modules/heartbeat/heartbeat.module).