public @NotNull BusyImpl getOrCreateBusy(UiActivity @NotNull ... activities) {
      Set<UiActivity> key = Set.of(activities);

      if (myActivities2Object.containsKey(key)) {
        return myActivities2Object.get(key);
      }
      return registerBusyObject(key);
    }
public @NotNull BusyImpl getOrCreateBusy(UiActivity @NotNull ... activities)