Update app.py

app.py

@@ -22,6 +22,9 @@ MODEL_OPTIONS = [
 ]
 
 def generate_text(input_text, selected_model, history):
+    if history is None:
+        history = ""  # Initialize history if it's None
+    
     response = requests.post(
         url="https://openrouter.ai/api/v1/chat/completions",
         headers={