If you haven’t figured it out, that blank name in the rankings is “http://.tumblr.com/”. There is nothing there. It is a typo made by enough people that Tumblr’s algorithm has indexed and given a pseudo-life. If you try to visit it, you get an error message.
Tumblr is telling me that (today) I’m as popular as a typo. I have such a loyal following that I draw comparable traffic to a random, non-existent web address. Or perhaps it isn’t random. Perhaps I’m comparably fascinating to the standard “Page Not Found” message at http://.tumblr.com. (By the way, do not click on that link. Popularity wise, I’m running neck and neck with .tumblr.com. If it gets any more traffic, the typo will pull ahead—and what will that do for my self-esteem?)