def _process_message(self, message: Message) -> None:
        """Featurizes the given message in-place.

        Args:
          message: a message to be featurized
        """
        if not self._feature_to_idx_dict:
            rasa.shared.utils.io.raise_warning(
                f"The {self.__class__.__name__} {self._identifier} has not been "
                f"trained properly yet. "
                f"Continuing without adding features from this featurizer."
            )
            return
        tokens = message.get(TOKENS_NAMES[TEXT])
        if tokens:
            sentence_features = self._map_tokens_to_raw_features(tokens)
            sparse_matrix = self._map_raw_features_to_indices(sentence_features)
            self.add_features_to_message(
                # FIXME: create sentence feature and make `sentence` non optional
                sequence=sparse_matrix,
                sentence=None,
                attribute=TEXT,
                message=message,
            )