private static @Nullable Object extractOldValueOrLog(@NotNull ObservableStateListener.PropertyChangeEvent event,
                                                       @SuppressWarnings("SameParameterValue") @Nullable Object fallbackValue) {
    Ref<@Nullable Object> oldValueRef = event.getOldValueRef();
    if (oldValueRef == null) {
      LOG.error("oldValueRef is expected not-null for the property: property name = " + event.getPropertyName());
      return fallbackValue;
    }
    return oldValueRef.get();
  }
private static @Nullable Object extractOldValueOrLog(@NotNull ObservableStateListener.PropertyChangeEvent event,
                                                       @SuppressWarnings("SameParameterValue") @Nullable Object fallbackValue)