class_docstr: Allows to filter any examples where no passage was selected to base the wizard reply
  on.
  
  This works best in flattened mode. E.g. run with: parlai display_data -t
  wizard_of_internet -n 100 -dt valid --mutators flatten+filter_no_passage_used
code: def many_episode_mutation(self, episode):
      out_episodes = []
      for e in episode:
          checked_sentences = e.get(CONST.SELECTED_SENTENCES)
          checked_sentences = " ".join(checked_sentences)
          if checked_sentences == CONST.NO_SELECTED_SENTENCES_TOKEN:
              pass
          else:
              out_episodes.append([e])
      return out_episodes
  
imports: import torch
  from parlai.core.mutators import register_mutator, MessageMutator, ManyEpisodeMutator
  from typing import Optional
  from parlai.core.opt import Opt
  from parlai.core.message import Message
  from parlai.core.params import ParlaiParser
  import parlai.tasks.wizard_of_internet.constants
  from parlai.tasks.wizard_of_wikipedia.mutators import AddLabel, AddLabelLM, CheckedSentenceAsLabel, AddCheckedSentence
label_desc: Use image node_id 1 for calling the WoiFilterNoPassageUsed obj's underlying member method code with example usage: obj.many_episode_mutation(episode) and returns: out_episodes