Gnus not recognizing IMAP select method

[mkbehr]

I'm new to Gnus, and I'm trying to use nnimap with an IMAP server on
localhost, but Gnus doesn't seem to be acknowledging its existence.
The Group buffer is completely empty, and the Server buffer only
contains the line "{nnfolder:archive} (closed)". I get no error
message or anything - it just doesn't seem to notice that the select
method exists. I've checked to make sure gnus-secondary-select-methods
is actually getting set (it is), and I'm not sure what else to do. How
can I fix this?
Here's my .gnus.el:
(setq mail-sources nil)
(setq gnus-select-method '(nnnil "")
      gnus-secondary-select-methods nil)
(add-to-list 'gnus-secondary-select-methods
 '(nnimap "localhost"
           (nnimap-address "localhost")
           (nnimap-port 143)
           (nnimap-authinfo-file "~/.authinfo")))

--
Michael Behr