Why is the result empty when applying filter to mongoose-paginate in NodeJS?

Here is the code It was working fine before I used same method in my other project but don't know what went wrong Note: if I don't apply filter then result is not empty.

async findAllCategories(req, res) {
    try {
      const { page = 1, perPage = 10, filter, sortField, sortDir } = req.query;
      const options = { page: parseInt(page, 10), limit: parseInt(perPage, 10) };
      const query = {};
      if (filter) {
            query.item = {
                $regex: filter
        }
      }
      if (sortField && sortDir) {
        options.sort = {
          [sortField]: sortDir
        }
      }
      console.log(query, options);
      const categories = await Category.paginate(query, options);
      return res.json(categories);
    } catch (err) {
      return res.status(INTERNAL_SERVER_ERROR).json(err);
    }
  }