private static List<? extends DownloadableLibraryFileDescription> getRequiredFiles(List<? extends DownloadableLibraryFileDescription> files) {
    return ContainerUtil.filter(files, (Condition<DownloadableLibraryFileDescription>)description -> !description.isOptional());
  }
private static List<? extends DownloadableLibraryFileDescription> getRequiredFiles(List<? extends DownloadableLibraryFileDescription> files)