@NotNull
  private Set<String> getUrls() {
    if (myUrls == null) {
      myUrls = new HashSet<>();
      for (VirtualFile file : myRootFiles) {
        String url = file.getUrl();
        myUrls.add(url);
      }
    }
    return myUrls;
  }
@NotNull
  private Set<String> getUrls()