How to use the konoha.word_tokenizers.WhitespaceTokenizer function in konoha

def _setup_tokenizer(self) -> None:
        if self._tokenizer == "character":
            self.tokenizer = word_tokenizers.CharacterTokenizer()

        if self._tokenizer == "whitespace":
            self.tokenizer = word_tokenizers.WhitespaceTokenizer()

        if self._tokenizer == "kytea":
            self.tokenizer = word_tokenizers.KyTeaTokenizer(
                with_postag=self.with_postag,
                model_path=self.model_path,
            )

        if self._tokenizer == "sentencepiece":
            if self.model_path is None:
                raise ValueError("`model_path` must be specified for sentencepiece.")

            self.tokenizer = word_tokenizers.SentencepieceTokenizer(
                model_path=self.model_path,
            )

        if self._tokenizer == "mecab":