docs: 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]}