@NotNull
  public final List<VirtualFile> showMergeDialog(List<? extends VirtualFile> files, MergeProvider provider) {
    return showMergeDialog(files, provider, provider.createDefaultMergeDialogCustomizer());
  }
@NotNull
  public final List<VirtualFile> showMergeDialog(List<? extends VirtualFile> files, MergeProvider provider)