Update app.py

app.py

@@ -550,7 +550,7 @@ with gr.Blocks(css=css) as demo:
         outputs=[output_html]
     )
     clear_btn.click(
-        fn=lambda: ("", "", None, "", ""),
+        fn=lambda: ("", "", None, "", None),
         inputs=[],
         outputs=[protein_seq, drug_seq, drug_idx, output_html, structure_file]
     )