Accessing emmentaler glyph-names in scheme

[tao_lilyponduser]

Hi lists,

I am trying to get glyphs from the emmentaler font as it is explained in the 
manual by the functions ly:system-font-load and ly:font-get-glyph.
So far it seems to work to access the glyphs and checking with ly:stencil? it 
tells me that I really got a stencil but when I try to use that stencil to 
override the stencil property of the NoteHead grob I get some errors I don't 
understand.

Any help is appreciated.

test =
#(define-music-function (parser location music) (ly:music?)
   (let* ((font (ly:system-font-load "emmentaler-20"))
          (glyph (ly:font-get-glyph font "noteheads.s2")))
         (display (ly:stencil? glyph))
         #{
                 \once \override NoteHead #'stencil = $glyph
                 $music
         #}))
   
<<
\test c'1
>>
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