docs: public static DbxThumbnailFormat bestForFileName(String fileName, DbxThumbnailFormat fallback)
      {
          fileName = fileName.toLowerCase();
          if (fileName.endsWith(".png") || fileName.endsWith(".gif")) {
              return DbxThumbnailFormat.PNG;
          }
          else if (fileName.endsWith(".jpeg") || fileName.endsWith(".jpg") || fileName.endsWith(".jpe")) {
              return DbxThumbnailFormat.JPEG;
          }
          return fallback;
      }