fix empty input bug

app.py

@@ -185,13 +185,15 @@ def _launch_demo(args):
 
     def add_text(history, task_history, text):
         task_text = text
-        if len(text) >= 2 and text[-1] in PUNCTUATION and text[-2] not in PUNCTUATION:
-            task_text = text[:-1]
+        history = history if history is not None else []
+        task_history = task_history if task_history is not None else []
         history = history + [(_parse_text(text), None)]
         task_history = task_history + [(task_text, None)]
         return history, task_history, ""
 
     def add_file(history, task_history, file):
+        history = history if history is not None else []
+        task_history = task_history if task_history is not None else []
         history = history + [((file.name,), None)]
         task_history = task_history + [((file.name,), None)]
         return history, task_history