Fixed the original code

app.py

@@ -17,7 +17,7 @@ gr.set_static_paths(paths=[Path.cwd().absolute()])
 @spaces.GPU(duration=100)
 def generate_song(reference_audio, lyrics_file, style_prompt, duration):
     # We need to save the uploaded files to temporary paths to pass to the model
-    reference_audio = reference_audio if reference_audio else None
+    reference_audio = reference_audio not in ("", None) and reference_audio or None
     
 
     # The model expects paths, so we write the prompt to a temp file if needed
@@ -64,7 +64,7 @@ with gr.Blocks() as demo:
     gr.Markdown("### Example Usage")
     gr.Examples(
         examples=[
-            [None, "gt0.json", "A sad, slow, acoustic country song", 30],
+            ["", "gt0.json", "A sad, slow, acoustic country song", 260],
         ],
         inputs=[reference_audio, lyrics_file, style_prompt, duration_slider],
         outputs=output_audio,