(describe-function): Don't pass `nil' as default.

1 files changed, 2 insertions, 1 deletions

diff --git a/lisp/help-fns.el b/lisp/help-fns.el
index 14ceacfd92f..32719275edd 100644
--- a/lisp/help-fns.el
+++ b/lisp/help-fns.el
@@ -113,7 +113,8 @@ With ARG, you are asked to choose which language."
      (setq val (completing-read (if fn
                                     (format "Describe function (default %s): " fn)
                                   "Describe function: ")
-                                obarray 'fboundp t nil nil (symbol-name fn)))
+                                obarray 'fboundp t nil nil
+                                (and fn (symbol-name fn))))
      (list (if (equal val "")
                fn (intern val)))))
   (if (null function)