Handle empty input folders

slider.py

@@ -26,6 +26,7 @@ def random():
 
 @app.route("/random_image/")
 def random_image():
+    try:
         last_modified_time, last_modified_file = max(
             (f.stat().st_mtime, f) for f in imgdir.glob(img_glob)
         )
@@ -35,6 +36,8 @@ def random_image():
         else:
             images = list(imgdir.glob(img_glob))
             selected_image = choice(images).relative_to(imgdir)
+    except ValueError:
+        return redirect(url_for("static", filename="clear.gif"))
 
     return redirect(
         url_for("image", filename=selected_image)