@Nullable
  protected ChangeDiffRequestChain.Producer getDiffRequestProducer(@NotNull Object userObject) {
    if (userObject instanceof Change) {
      return ChangeDiffRequestProducer.create(myProject, (Change)userObject);
    }
    return null;
  }
@Nullable
  protected ChangeDiffRequestChain.Producer getDiffRequestProducer(@NotNull Object userObject)