Test patch for None teacher old

biscuit/apps/untis/sub.py

@@ -76,12 +76,17 @@ class Substitution(object):
         # print(db_obj.teacher_idlessn)
         if db_obj.teacher_idlessn != 0:
             self.teacher_old = drive["teachers"][db_obj.teacher_idlessn]
+
         if db_obj.teacher_idsubst != 0:
             self.teacher_new = drive["teachers"][db_obj.teacher_idsubst]
 
             if self.teacher_old is not None and self.teacher_new.id == self.teacher_old.id:
                 self.teacher_new = None
 
+            if self.teacher_old is None and self.teacher_new is not None:
+                self.teacher_old = self.teacher_new
+                self.teacher_new = None
+
         self.lesson_element, self.room_old = get_lesson_element_by_id_and_teacher(self.lesson_id, self.teacher_old,
                                                                                   self.lesson, self.date.weekday() + 1)
         # print(self.lesson)