File "/home/jan/Programmierung/tryton-3.0.2/tryton/gui/window/view_form/view/calendar_gtk/parser.py", line 56, in on_event_released
    record.save()

  File "/home/jan/Programmierung/tryton-3.0.2/tryton/gui/window/view_form/model/record.py", line 325, in save
    if self.parent:

  File "/home/jan/Programmierung/tryton-3.0.2/tryton/gui/window/view_form/model/record.py", line 157, in parent
    return self.group.parent

'NoneType' object has no attribute 'parent'