Adds a match key/value

def _add_match(self, match_key, match_value, match):
        """Adds a match key/value"""
        if match_key is None:
            raise NullArgument()
        if match is None:
            match = True
        if match:
            inin = '$in'
        else:
            inin = '$nin'
        if match_key in self._query_terms:
            if inin in self._query_terms[match_key]:
                self._query_terms[match_key][inin].append(match_value)
            else:
                self._query_terms[match_key][inin] = [match_value]
        else:
            self._query_terms[match_key] = {inin: [match_value]}