The api cannot list the contribs from [[de:User:0]], the api says "User parameter may not be empty" (see URL). The user exist (http://de.wikipedia.org/w/api.php?action=query&list=users&ususers=0)
Version: unspecified
Severity: enhancement
URL: http://de.wikipedia.org/w/api.php?action=query&list=usercontribs&ucuser=0