/// <summary>
 /// Returns stream with content of thumbnail image for request album item.
 /// </summary>
 /// <param name="thumbSize">Max requested thumbnail size.</param>
 public abstract AlbumItemContentResult GetThumbnail(Album album, string contentItemId, Size thumbSize, bool enforceAspectRatio = true);
 public AlbumItemContentResult(Stream contentStream, Size? size, string mimeType)
 {
     Stream = contentStream;
     Size = size;
     MimeType = mimeType;
 }