The feed does have a title or subtitle. I don't have Jekyll installed, otherwise I'd test this, but I think there are two simple edits in feed.xml :
Line seven should probably be
<title>{{ site.title }}</title>
And line 10 should probably be
<description>{{ site.subtitle }}</description>
Right now they have blog_ included, which isn't defined anywhere I can see.
I would submit code, but I am not 100% sure that is how Jekyll works.