// ...
const getModule = (config) => {
  const documentClient = new AWS.DynamoDB.DocumentClient(config)

  return ({
    // ...
    getByPK: (params, attributes = undefined) =>
      documentClient
        .get(
          mergedParams(params, attributes ? projectionExpression(attributes) : {})
        )
        .promise()
        .then(data => (Object.keys(data).length ? data.Item : undefined))
  })
}
// ...