Update ch.py

ch.py

@@ -13,7 +13,7 @@ if s=="enter chat bot":
     time.sleep(5)
     model=l.GoogleGenerativeAI(model="gemini-2.5-flash-lite",api_key=api,max_tokens=10,temperature=0.2)
     if not st.session_state:
-        st.session_state["messages"]=[["system",f"behave like a 1 year experice chat model trainer of {st.session_state["topic"]} Topic you strictly should not discuss anything other that specified topic"]]
+        st.session_state["messages"]=[["system",f"behave like a 1 year experice chat model trainer of {st.session_state.get("topic")} Topic you strictly should not discuss anything other that specified topic"]]
         prompt=st.chat_input("Type your message")
         if prompt:
             st.session_state["messages"].append(["user",prompt])