docs: protected void setRequestHeaders(final URLConnection connection, final SyndFeedInfo syndFeedInfo, final String userAgent) {
          if (syndFeedInfo != null) {
              // set the headers to get feed only if modified
              // we support the use of both last modified and eTag headers
              if (syndFeedInfo.getLastModified() != null) {
                  final Object lastModified = syndFeedInfo.getLastModified();
                  if (lastModified instanceof Long) {
                      connection.setIfModifiedSince((Long) syndFeedInfo.getLastModified());
                  }
              }
              if (syndFeedInfo.getETag() != null) {
                  connection.setRequestProperty("If-None-Match", syndFeedInfo.getETag());
              }
  
          }
          // header to retrieve feed gzipped
          connection.setRequestProperty("Accept-Encoding", "gzip");
          connection.addRequestProperty("User-Agent", userAgent);
  
          if (isUsingDeltaEncoding()) {
              connection.addRequestProperty("A-IM", "feed");
          }
      }