code: private ImmutableSet<File> findGeneratedFilesInDirectory(File directory) throws IOException {
      if (directory == null || !directory.isDirectory())
        return ImmutableSet.of();
      List<File> sourceFilesInDirectory = getFiles(directory, "**/*.java", null);
      sourceFilesInDirectory.addAll(getFiles(directory, "**/*.scala", null));
      return ImmutableSet.copyOf(sourceFilesInDirectory);
    }
docs: Find all {@code .java} and {@code .scala} files in the given directory.