[plt-scheme] r6rs mode, empty nongenerative forms

Ciao,

  it seems to  me that PLT version 4.2.4  does not allow the
NONGENERATIVE auxiliary syntax to  be used without value, as
in:

  (define-record-type (:sentinel make-sentinel sentinel?)
    (opaque #t)
    (sealed #t)
    (nongenerative))

while  R6RS states  that this  is  possible and  the uid  is
automatically  generated at  expansion time.   I do  not see
this incompatibility listed at

     <http://docs.plt-scheme.org/r6rs/conformance.html>

can it be added?

TIA
-- 
Marco Maggi