code: function getDynamoDBDocClientOptionsUsed(region) {
    const regionKey = getRegionKey(region);
    return regionKey ? dynamoDBDocClientOptionsByRegionKey.get(regionKey) : undefined;
  }
docs: Gets the DynamoDB.DocumentClient options used to construct 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 options used to construct the
  DynamoDB.DocumentClient instance cached for the given or current region (if any); otherwise returns undefined