protected void showChangesBetweenRevisions(@NotNull final FilePath path, @NotNull final T older, @Nullable final T newer) {
    if (newer == null) {
      FileDocumentManager.getInstance().saveAllDocuments();
    }
    new CollectChangesTask(VcsBundle.message("file.history.diff.handler.comparing.process")) {

      @NotNull
      @Override
      public List<Change> getChanges() throws VcsException {
        return getChangesBetweenRevisions(path, older, newer);
      }

      @NotNull
      @Override
      public String getDialogTitle() {
        return getChangesBetweenRevisionsDialogTitle(path, older, newer);
      }
    }.queue();
  }
protected void showChangesBetweenRevisions(@NotNull final FilePath path, @NotNull final T older, @Nullable final T newer)