why is not 3.X?

in v3
net.jforum.entities.Category
repository always is null

While I don't understand what you mean by "why is not 3.X", if this question is about the beta version of JForum 3, then please note that these forums here are about a fork of the original JForum 2. I don't think there are any forums dedicated to the JForum 3 beta, but you can try your luck at the JForum forum at JavaRanch. But also note that JForum 3 is unfinished, and thus it's unlikely to be in use anywhere, so there are probably no people out there who can help you (unless you contact the developer directly).