Fix constraints

aleksis/core/models.py

@@ -1707,10 +1707,16 @@ class CalendarEvent(CalendarEventMixin, ExtensiblePolymorphicModel, RecurrenceMo
                 name="datetime_end_or_date_end",
             ),
             models.CheckConstraint(
-                check=Q(datetime_end__gte=F("datetime_start")), name="datetime_start_before_end"
+                check=Q(datetime_end__gte=F("datetime_start"))
+                | Q(datetime_start__isnull=True)
+                | Q(datetime_end__isnull=True),
+                name="datetime_start_before_end",
             ),
             models.CheckConstraint(
-                check=Q(date_end__gte=F("date_start")), name="date_start_before_end"
+                check=Q(date_end__gte=F("date_start"))
+                | Q(date_start__isnull=True)
+                | Q(date_end__isnull=True),
+                name="date_start_before_end",
             ),
             models.CheckConstraint(
                 check=~(Q(datetime_start__isnull=False, timezone="") & ~Q(recurrences="")),