code: async function decodeData (record) {
      // convert null values to undefined
      for (const key of Object.keys(record)) {
          if (record[key] === null) {
              record[key] = undefined
          }
      }
      // get data column to decode data
      var dataColumn = this.columnName('data')
      // skip if no data column
      if (!defined(dataColumn) || !defined(record[dataColumn])) {
          return
      }
      // decompress if compresion in use
      if (this.compression) {
          // decompress data
          record[dataColumn] = await snappyUncompress(Buffer.from(record[dataColumn], 'base64'), {asBuffer: false})
      }
      // decode data
      record[dataColumn] = JSON.parse(record[dataColumn])
  }
docs: @function decodeData
  
  decode data stored in database and return object
  
  @param {object} record
  
  @returns {Promise}