Exception calling 'theme_boost_union_before_session_start'

• line 200 of /cache/classes/factory.php: call to core_cache\factory->create_definition()
• line 190 of /cache/classes/cache.php: call to core_cache\factory->create_cache_from_definition()
• line 2386 of /theme/boost_union/locallib.php: call to core_cache\cache::make()
• line 808 of /theme/boost_union/lib.php: call to theme_boost_union_manipulate_hooks()
• line 900 of /lib/setup.php: call to theme_boost_union_before_session_start()
• line 881 of /config.php: call to require_once()
• line 29 of /course/format/onetopic/styles.php: call to require_once()