No module api file after generating ruby core api

I want to generate a local version of ruby core api.
And I am using the hanna
tool(GitHub - mislav/hanna: More than just a new RDoc template) to generate the api.

I downloaded the newest version of ruby 1.9.1 and uncompress it in a
local dir.
After that, I just run

hanna -a -o

The process went well, and core api were generated.
However, when I want to look an api, say ‘extended(Module)’, the browser
only tell me ‘can not find file Module.html#M002890’

Can anybody please help me?

Why is this happening? and How can I generate core api including the
Module api file?