OSIS-1170 Treat case when no container year  (list xlsx)
OSIS-1170 Treat case when no container year  (list xlsx)

	modified:   base/business/learning_unit.py

uclouvain/osis_louvain,uclouvain/osis,uclouvain/OSIS-Louvain,uclouvain/OSIS-Louvain,uclouvain/osis_louvain,uclouvain/OSIS-Louvain,uclouvain/osis,uclouvain/osis,uclouvain/osis,uclouvain/osis_louvain