[Exim] another Exim 4.10 question

Hello,

here's something else that is troubling me:

NIS_EXISTS = ${lookup {$local_part} nis {passwd.byname} }
NIS_USER = ${extract{3}{:}{ ${lookup {$local_part} nis {passwd.byname} } }}
NIS_HOME = ${extract{6}{:}{ ${lookup {$local_part} nis {passwd.byname} } }}

begin routers

procmail:
driver = accept
condition = NIS_EXISTS
debug_print = ${local_part}:NIS_HOME/.procmailrc
require_files = ${local_part}:NIS_HOME/.procmailrc
user = NIS_USER
group = mail
transport_home_directory = NIS_HOME
no_verify
no_expn
transport = procmail_pipe

this, I think, would allow NIS & NFS only users to use procmail on the
mailhost without having accounts there

now, debug_print outputs:
bill:/home/big/bill/.procmailrc

while require_files outputs:
failed to expand "${extract{6}{" for require_files: missing } at end of string


thanks

Bill - bill@???