aligning lyrics to hidden notes

[Sandro Santilli]

I've been trying for some time now to align lyrics
to an hidden melody but when I try that all the rests
end up attached to the bottom line of the pentagram,
which looks like a bug in lilypond itself, can anyone
see if that's the case (a bug) or I'm doing something
wrong ?

Here's the .ly file:
http://strk.kbt.io/tmp/quizas-broken-basspart.ly

This is a summary of offending section (look for
"bassPart" in the .ly above for the actual section):

    bassPart = {
    <<

      \new Staff {
        <<

        % UNCOMMENTING THE LINE BELOW
        % MOVES ALL RESTS TO THE BOTTOM !!
        %\new NullVoice = "vocal" { \melody }

        \new Voice = "bass" { \bassline }
        >>
      }

      %\new Lyrics \lyricsto "vocal" \words_line_one
    >>
    }

I cannot attach "words_line_one" to "vocal" NullVoice
unless I define it...

Can anyone help me making my bass player aware of lyrics ? :)

Thanks in advance !

--strk;