Update app.py

app.py

@@ -14,7 +14,7 @@ def clip(yt_url, video_file_path, start_timestamp, end_timestamp):
     duration = int(end_timestamp) - int(start_timestamp)
     
     with TemporaryDirectory() as tmpdir:
-        if yt_url is not None:
+        if yt_url is not None and len(yt_url.strip()) != 0:
             video_output_path = os.path.join(tmpdir, "video.mp4")
             ydl_opts = {
                 "quiet": True,