Null - safe way of TeacherLecturePreference in scheduling
Merge commit 'dfcc8e63178a6f0818d939ccbab2d7a8ec291321'
Merge Fix
Merge branch 'master' of https://github.com/CalZoneVUB/CalZone into TimFrondEnd
Merge branch 'master' of https://github.com/CalZoneVUB/CalZone

# By MPieter (1) and Timbo925 (1)
# Via Timbo925 (2) and MPieter (1)
* 'master' of https://github.com/CalZoneVUB/CalZone:
  Merge Fix
  Null - safe way of TeacherLecturePreference in scheduling