TypeError: '>' not supported between instances of 'datetime.datetime' and 'NoneType'

[fuzzylogic2000]

https://sentry.liqd.net/sentry/product-dev/issues/800/

TypeError: 'Project' object is not subscriptable
  File "django/template/base.py", line 829, in _resolve_lookup
    current = current[bit]

TypeError: '>' not supported between instances of 'datetime.datetime' and 'NoneType'
(28 additional frame(s) were not displayed)
...
  File "django/template/base.py", line 671, in resolve
    obj = self.var.resolve(context)
  File "django/template/base.py", line 796, in resolve
    value = self._resolve_lookup(context)
  File "django/template/base.py", line 837, in _resolve_lookup
    current = getattr(current, bit)
  File "django/utils/functional.py", line 80, in __get__
    res = instance.__dict__[self.name] = self.func(instance)
  File "adhocracy4/projects/models.py", line 407, in end_date
    if last_event.date > end_date:

Internal Server Error: /musterstadt/

[fuzzylogic2000]

fixed in a4