I think this is a little confusing, couldn't we just do this:

if (StringUtils.isBlank(marker)) {
   response = getFeedHead(...)
} else {
   if (marker.equals(MOCK_LAST_MARKER) {
      response = getLastPage(getFeedRequest, pageSize);
   } else {
      response = getFeedPage(getFeedRequest, marker, pageSize);
   }
}

I'm not sure if that improves performance or anything, just seems to read a little better to me. What do you think?