docs: ContentMatcher remove(
      Conjunction selector,
      MatchTarget object,
      InternTable subExpr,
      OrdinalPosition parentId)
      throws MatchingException
    {
      if (vacantChild == null)
        throw new IllegalStateException();
      vacantChild =
        vacantChild.remove(selector, object, subExpr, ordinalPosition);
      return vacantChild;
    }