fixup! Rewrite internal arc

Author: Marenz

src/frequenz/dispatch/actor.py

@@ -266,10 +266,11 @@ def _schedule_start(self, dispatch: Dispatch) -> None:
             return
 
         # Schedule the next run
-        next_run = dispatch.next_run
-        assert next_run is not None
-        heappush(self._scheduled_events, (next_run, dispatch))
-        _logger.debug("Scheduled dispatch %s to start at %s", dispatch, next_run)
+        if next_run := dispatch.next_run:
+            heappush(self._scheduled_events, (next_run, dispatch))
+            _logger.debug("Scheduled dispatch %s to start at %s", dispatch.id, next_run)
+        else:
+            _logger.debug("Dispatch %s has no next run", dispatch.id)
 
     def _schedule_stop(self, dispatch: Dispatch) -> None:
         """Schedule a dispatch to stop.