CI_DB_mysqli_result->_fetch_object()

Stack trace:
#0 /home/system/database/DB_result.php(259): CI_DB_mysqli_result->_fetch_object()
#1 /home/system/database/DB_result.php(409): CI_DB_result->result_object()
#2 /home/system/database/DB_result.php(335): CI_DB_result->row_object(0)
#3 /home/system/libraries/Session/drivers/Session_database_driver.php(425): CI_DB_result->row()
#4 /home/system/libraries/Session/drivers/Session_database_driver.php(282): CI_Session_database_driver->_release_lock()
#5 [internal function]: CI_Session_database_driver->close()
#6 [internal function]: session_write_close()
#7 {main}

Any have ideas?