code: @VisibleForTesting
    Optional<String> buildQuery(String folderId, String fileName) {
      if (StringUtils.isEmpty(folderId) && StringUtils.isEmpty(fileName)) {
        return Optional.absent();
      }
  
      StringBuilder query = new StringBuilder();
      if (StringUtils.isNotEmpty(folderId)) {
        query.append("'").append(folderId).append("'")
             .append(" in parents");
      }
      if (StringUtils.isNotEmpty(fileName)) {
        if (query.length() > 0) {
          query.append(" and ");
        }
        query.append("name contains ")
             .append("'").append(fileName).append("'");
      }
      return Optional.of(query.toString());
    }
docs: Build query for Google drive.
  @see https://developers.google.com/drive/v3/web/search-parameters
  
  @param folderId
  @param fileName
  @return Query