public static @Nullable File findCommonAncestor(@NotNull Collection<? extends Change> changes) {
    File ancestor = null;
    for (Change change : changes) {
      File currentChangeAncestor = getCommonBeforeAfterAncestor(change);
      if (currentChangeAncestor == null) return null;
      if (ancestor == null) {
        ancestor = currentChangeAncestor;
      }
      else {
        ancestor = FileUtil.findAncestor(ancestor, currentChangeAncestor);
        if (ancestor == null) return null;
      }
    }
    return ancestor;
  }
public static @Nullable File findCommonAncestor(@NotNull Collection<? extends Change> changes)