public List<File> getLeafFolders(@NonNull String extension, List<File>... importFolders) {
List<File> results = Lists.newArrayList();
if (importFolders != null) {
for (List<File> folders : importFolders) {
SourceSearcher searcher = new SourceSearcher(folders, extension);
searcher.setUseExecutor(false);
LeafFolderGatherer processor = new LeafFolderGatherer();
try {
searcher.search(processor);
} catch (InterruptedException e) {
// wont happen as we're not using the executor, and our processor
// doesn't throw those.
} catch (ExecutionException e) {
// wont happen as we're not using the executor, and our processor