(file-relative-name): Don't lose when DIRECTORY is nil.

1 files changed, 2 insertions, 1 deletions

diff --git a/lisp/files.el b/lisp/files.el
index 0e14d0027f2..0a0052a01ae 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -940,7 +940,8 @@ Value is a list whose car is the name for the backup file
 (defun file-relative-name (filename &optional directory)
   "Convert FILENAME to be relative to DIRECTORY (default: default-directory)."
   (setq filename (expand-file-name filename)
-        directory (file-name-as-directory (or (expand-file-name directory)
+        directory (file-name-as-directory (if directory
+                                              (expand-file-name directory)
                                               default-directory)))
   (while (not (string-match (concat "^" (regexp-quote directory)) filename))
     (setq directory (file-name-directory (substring directory 0 -1))))