code: function getDynamoDBSequenceNumber(record) {
    return record && record.dynamodb && record.dynamodb.SequenceNumber ? record.dynamodb.SequenceNumber : '';
  }
docs: Returns the sequence number from the given DynamoDB stream event record.
  @param {DynamoDBEventRecord|*} record - a DynamoDB stream event record
  @returns {string} the sequence number (if any) or an empty string