Update app.py

app.py

@@ -81,6 +81,9 @@ def generate(
     top_k: int = 20,
     repetition_penalty: float = 1.0,
 ) -> Iterator[str]:
+    if chat_history is None:
+        chat_history = []
+
     conversation = []
     if model_choice == "Storytell":
         model = storytell_model
@@ -88,7 +91,7 @@ def generate(
     else:
         model = editing_model
         tokenizer = editing_tokenizer
-
+    
     # Checking each tuple in chat_history to ensure it has exactly two elements
     for item in chat_history:
         if isinstance(item, tuple) and len(item) == 2: