group in the mail-sources could not get mails

[Yong <leapfrog.cc@gmail.com>]

Hi,

I use maildrop to deliver my mails to maildir directories,
and use nnml as mail backend in Gnus.
Because maildrop had taken care of the mail splitting,
I don't want Gnus to splitting mails again.
So I set the mail-sources variable to "group" in .gnus.el:

(setq mail-sources '((group)))

then use "G p" in the *Group* buffer to set the parameter of the group
where I want my mails to go:

((mail-source . (maildir :path "/path/to/maildir")))

However, this group can't get the mails. And when I use "G c" to see
the group parameters, I got:

Unknown entries:
INS DEL Lisp expression: 
(mail-source maildir :path "/path/to/maildir")



BTW, if I just use

(setq mail-sources '((maildir :path "/path/to/maildir")))

then Gnus get the mails normally.

I'm using Gnus v5.13 and Emacs 24.3.
Is there something wrong with my .gnus.el configuration? 


Thanks,

Yong