foo should not have text (all data is in attributes)

You have an old-style link in your Atom feed.

In Atom 0.3, the format of link changed. Instead of simply containing an address of a page or resource, it now contains three attributes that describe the type of link, and the MIME type of the linked resource, and the address of the resource.

This was the format in Atom 0.2:

<link>http://www.example.com/</link>

This is the new format in Atom 1.0 and later:

<link href="http://www.example.com/"/>

Note: this information only applies to Atom feeds (not RSS feeds).