def _append_to_term_value(self, c: str):
        """
        If the term type is IN, append c to the last list in term_value.
        Otherwise, append c to term_value.

        For IN terms, term_value is a list of lists.
        """
        if self._term_type == MarqoFilterStringParser._TermType.In:
            self._term_value[-1].append(c)
        else:
            self._term_value.append(c)

        If the term type is IN, append c to the last list in term_value.
        Otherwise, append c to term_value.

        For IN terms, term_value is a list of lists.
        
src/marqo/core/search/search_filter.py