private List <CloudBlobDirectory> GetFolders(string containerName, CloudBlobDirectory blobDirectory = null)
        {
            if (blobDirectory == null)
            {
                var container = GetContainer(containerName);
                var items     = container.GetItems(string.Empty).Result;
                return(items.OfType <CloudBlobDirectory>().ToList());
            }
            var children = blobDirectory.GetItems().Result;

            return(children.OfType <CloudBlobDirectory>().ToList());
        }