Invalid answers are removed multiple times which results in key errors

Class Question got a method remove_answers that is called by remove_invalid_answer_sets of class DataContainer multiple times which results in key errors:

def remove_answers(self, participant_ids: Set[str]) -> None:
  """
  Remove the answers by the specified participants.
    Args:
      participant_ids:
        The IDs of the participants whose answers are to be removed.
        Invalid IDs are ignored.
  """
  for participant_id in participant_ids:
    del self._answers[participant_id]