Lessons without any groups are displayed as cancelled if there is any event in the same time period

added part::backend source::customer type::bug labels

assigned to @hansegucker

created branch 184-lessons-without-any-groups-are-displayed-as-cancelled-if-there-is-any-event-in-the-same-time to address this issue

mentioned in merge request !277 (merged)

closed with merge request !277 (merged)

mentioned in commit dc71a5a9