Improve error when wallpaper-command is nil

* lisp/image/wallpaper.el (wallpaper-set): Improve the error message
when 'wallpaper-command' is nil.

diff --git a/lisp/image/wallpaper.el b/lisp/image/wallpaper.el
index d024d6238cb5bd7e1f0d91e31aea1e0885468367..fe6882a5880d80bb919056c38138a9ef5f668e25 100644 (file)
--- a/lisp/image/wallpaper.el
+++ b/lisp/image/wallpaper.el
@@ -254,6 +254,8 @@ On Haiku, no external command is needed, so the value of
         ((featurep 'haiku)
          (haiku-set-wallpaper file))
         (t
+         (unless wallpaper-command
+           (error "Couldn't find a command to set the wallpaper with"))
          (let* ((fmt-spec `((?f . ,(expand-file-name file))
                             (?h . ,(wallpaper--get-height-or-width
                                     "height"