gexf and Viz Property Problem: XMLStreamException: ParseError ElementPrefixUnbound?viz&viz:position

[IjonTichyRaumpilot]

I added a viz position to the gexf File and was wondering why I got an error message ...XMLStreamException: ParseError ... ElementPrefixUnbound?viz&viz:position when I tried to open it in gephi.
I found out that the header was missing the entry
xmlns:viz="http://www.gexf.net/1.1draft/viz" version="1.1"
and this was due to a missing setVisualisation(true)

So I had to add something like this:
Gexf gexf = new GexfImpl();
// Contains Visualisation
gexf.setVisualization(true);

And got a proper gexf File.