def _join_term_value(self, term_value: Union[List[str], List[List[str]]]) -> Union[str, List[str]]:
        """
        If the term type is IN, join every list in term_value
        Otherwise, join term_value.

        For IN terms, term_value is a list of lists.
        """
        if self._term_type == MarqoFilterStringParser._TermType.In:
            return [''.join(item) for item in term_value]
        else:
            return ''.join(term_value)

        If the term type is IN, join every list in term_value
        Otherwise, join term_value.

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