class_docstr: Adds the checked sentence to the end of the text.
  
  But only a single time.
class_docstr_tok: ["Adds","the","checked","sentence","to","the","end","of","the","text",".","But","only","a","single","time","."]
code: def message_mutation(self, message: Message) -> Message:
      new_message = message.copy()
      if "text" not in message:
          return message
      text = new_message.pop("text")
      checked_sentence = new_message.get(
          self.checked_sentence_kword, ""
      )
      if isinstance(checked_sentence, list):
          checked_sentence = " ".join(checked_sentence)
  
      text += f"\n{CONST.KNOWLEDGE_TOKEN} {checked_sentence} {CONST.END_KNOWLEDGE_TOKEN}"
      new_message["text"] = text
  
      return new_message
  
imports: from parlai.core.mutators import register_mutator, MessageMutator, ManyEpisodeMutator
  from parlai.core.message import Message
  import parlai.tasks.wizard_of_internet.constants
  import random
label_desc: Use image node_id 2 for calling the AddCheckedSentence obj's underlying member method code with example usage: obj.message_mutation(message) and returns: new_message, message