private @NotNull BusyImpl registerBusyObject(@NotNull Set<UiActivity> key) {
      final BusyImpl busy = createBusyImpl(key);
      myActivities2Object.put(key, busy);
      myObject2Activities.put(busy, key);
      return busy;
    }
private @NotNull BusyImpl registerBusyObject(@NotNull Set<UiActivity> key)