Update app.py

app.py

@@ -252,7 +252,8 @@ def ask_llm(system, user_input):
 def ask_llm_stream(system, user_input):
     llm_response = ""
     client = Groq(api_key=os.environ["GROQ_KEY"])
-
+    if user_input is None or user_input == "":
+        user_input = "What is the introduction of the document about?"
     messages = [
         {
             "role": "system",