RDoc doesn't create diagrams

Hi guys,

I’m having a problem with rdoc.
When I use the --diagrams CLI argument no diagrams are generated without
any notification or error message.

ruby 1.9.2p0 (2010-08-18) [x86_64-linux]
rdoc 2.5.8

Does anyone have any experience with that?

Cheers,
Tasos L.