(pop-up-frame-function): Remove choice nil since it

does not represent a valid value.

lisp/ChangeLog

+2009-05-02  Martin Rudalics  <rudalics@gmx.at>
+
+	* frame.el (pop-up-frame-function): Remove choice nil since it
+	does not represent a valid value.
+
 2009-04-30  David Reitter  <david.reitter@gmail.com>
 	* term/ns-win.el (ns-make-command-string, ns-grabenv)

lisp/frame.el

@@ -120,7 +120,7 @@ affected by this variable."
 This function is called with no arguments and should return a new
 frame.  The default value calls `make-frame' with the argument
 `pop-up-frame-alist'."
-  :type '(choice (const nil) (function :tag "function"))
+  :type 'function
   :group 'frames)
 
 (defcustom special-display-frame-alist