https://fedorahosted.org/389/ticket/47659 https://fedorahosted.org/389/attachment/ticket/47659/0001-Ticket-47659-ld... Bug description: A suffix mapping tree could exist without the corresponding backend. The existing code did not properly check the backend returned from slapi_mapping_tree_find_backend_for_sdn. When NULL backend is returned, it triggers the NULL pointer dereference. Fix description: This patch added a NULL backend check to usn_get_last_usn, and moved a logging to the if clause where the backend is not NULL.