@Nullable
  private static Module findParentModule(@Nullable Project project, VirtualFile @NotNull [] files) {
    if (project == null) return null;
    Module result = null;
    ProjectFileIndex index = ProjectFileIndex.getInstance(project);
    for (VirtualFile file : files) {
      Module module = index.getModuleForFile(file, false);
      if (module == null) return null;
      if (result == null) {
        result = module;
      }
      else if (!result.equals(module)) {
        return null;
      }
    }
    return result;
  }
@Nullable
  private static Module findParentModule(@Nullable Project project, VirtualFile @NotNull [] files)