code: def files_missing_substring(file_names, substring):
      for file_name in file_names:
          with open(file_name, "r", encoding="utf-8") as current_file:
              content = current_file.read()
  
              if content.strip() and substring not in content:
                  yield file_name
  
label_desc: Use image node_id 2 for calling a global function with example usage: files_missing_substring(file_names, substring) without return types