Jdom 2 xpath query

Question

I'm trying to parse the following file:

<root>
   <gaja boa='true' feia='false'>
      ...
   </gaja>
   <gaja>
      ...
   </gaja>
   <gaja feia='true'>
      ...
   </gaja>
</root>

I'm looking for gaja element without attribute feia or with feia='false',this is the query I'm using /root/gaja[not(@feia) or (@feia='false')]

In this website I tested the query and the results were as expected, but in my java program I don't have these results.

I'm using jdom 2.0.6. Does it have the not function?