model.swift

    private func loadArticle(folderURL: NSURL) -> HelpCentreArticle? {

        let metadataURL = folderURL.URLByAppendingPathComponent(ArticleMetadataFileName)
        if (!metadataURL.checkResourceIsReachableAndReturnError(nil)) {
            return nil
        }

        let maybeMetadata = NSData(contentsOfURL: metadataURL)
        guard let rawMetadata = maybeMetadata else {
            return nil
        }

        let metadata = try? NSJSONSerialization.JSONObjectWithData(rawMetadata, options: []) as? [String : AnyObject]

        guard let title = metadata??[ArticleMetadataTitleKey] as? String,
            identifier = metadata??[ArticleMetadataIdentifierKey] as? String,
            categoryName = metadata??[ArticleMetadataCategoryKey] as? String else {
                return nil
        }

        return HelpCentreArticle(title: title,
                                 identifier: identifier,
                                 iconName: metadata??[ArticleMetadataIconKey] as? String,
                                 categoryName: categoryName, baseURL: folderURL)
    }