Test deleting values

src/icalendar/alarms.py

@@ -282,8 +282,7 @@ def acknowledge_until(self, dt: Optional[date]) -> None:
         an event has been acknowledged because of an alarm.
         All alarms that happen before this time count as ackknowledged.
         """
-        if dt is not None:
-            self._last_ack = tzp.localize_utc(dt)
+        self._last_ack = tzp.localize_utc(dt) if dt is not None else None
 
     def snooze_until(self, dt: Optional[date]) -> None:
         """This is the time in UTC when all the alarms of this component were snoozed.
@@ -293,8 +292,7 @@ def snooze_until(self, dt: Optional[date]) -> None:
         The alarms are supposed to turn up again at dt when they are not acknowledged
         but snoozed.
         """
-        if dt is not None:
-            self._snooze_until = tzp.localize_utc(dt)
+        self._snooze_until = tzp.localize_utc(dt) if dt is not None else None
 
     def set_local_timezone(self, tzinfo:Optional[tzinfo|str]):
         """Set the local timezone.

src/icalendar/tests/test_issue_716_alarm_time_computation.py

@@ -338,4 +338,10 @@ def test_rfc_9074_alarm_times(events, event_index, alarm_times):
 
 def test_set_to_None():
     """acknowledge_until, snooze_until, set_local_timezone."""
-    pytest.skip("TODO")
+    a = Alarms()
+    a.set_start(None)
+    a.set_end(None)
+    a.set_local_timezone(None)
+    a.acknowledge_until(None)
+    a.snooze_until(None)
+    assert vars(a) == vars(Alarms())