[pdftex] hyperref and chapter with empty names

[Turlupin]

Hello,

I use hyperref to have the "bookmarks" in a pdfreader.
My text has chapter with empty name, in the table of content i have
something like that :

I.............
II...........
III..........

(i'm use \Roman)

The best would be to have something like "Chapter I" instead of "I", my most
important problem is that in the bookmarks, chapters appear as "undefined"
(on acrobat reader for example, or in the sony reader)

Tanks,