docs: function cleanUpFalsyCsvValue(rows) {
    for (let i = 0; i < rows.length; i++) {
      for (let j = 0; j < rows[i].length; j++) {
        // analyzer will set any fields to 'string' if there are empty values
        // which will be parsed as '' by d3.csv
        // here we parse empty data as null
        // TODO: create warning when deltect `CSV_NULLS` in the data
        if (!rows[i][j] || CSV_NULLS.includes(rows[i][j])) {
          rows[i][j] = null;
        }
      }
    }
  }