docs: def generate_sources_zip(milestone_id=None, output=None):
      """
      Generate a sources archive for given milestone id. 
      """
      if not is_input_valid(milestone_id, output):
          logging.error("invalid input")
          return 1
      create_work_dir(output)
      download_sources_artifacts(milestone_id, output)
      create_zip(output)