Docbase raises IllegalArgumentException (possibly broken)

When using the Docbase primitive element.

STEPS:
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• Create Namespace (mynamespace|http://www.ns.net/01)
• Update All Content
• Create Document Type (mydoctype)
• Insert Docbase
• Save&Done
• Update all Content
• Create Root Folder (myfolder)
• Create Document (mydoc < mydoctype)
• Click [...] in Docbase in 'mydoc'

EXPECTED:
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something like a dialog opening that lets the user pick up a document

ACTUAL:
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nothing obvious apparently takes place, but the messages (see attached 'error') at the Tomcat Console.