code: function getDynamoDBDocClient(region) {
    const regionKey = getRegionKey(region);
    return regionKey ? dynamoDBDocClientByRegionKey.get(regionKey) : undefined;
  }
docs: Gets the DynamoDB.DocumentClient instance cached for the given region (if specified and if previously cached);
  otherwise for the current region (if previously cached); otherwise returns undefined.
  @param {string} [region] - the optional AWS region to use - defaults to current AWS region if not specified
  @returns {AWS.DynamoDB.DocumentClient|undefined} the DynamoDB.DocumentClient instance cached for the given or current
  region (if any); otherwise returns undefined