chatstate fix

src/chatbot_backend.py

@@ -27,8 +27,8 @@ class ChatState(TypedDict):
     doc_content: Optional[str]      # User's uploaded document content
     search_enabled: bool         # Whether to use external search
     model_choice: str            # Model selected ("OpenAI (Paid)" or "LLaMA (Open Source)")
-    doc_source: str | None       # Document source ("Upload Your Documents" or "Use Sample Documents")
-    system_prompt: str | None     # ✅ New field for system prompt
+    doc_source: Optional[str]       # Document source ("Upload Your Documents" or "Use Sample Documents")
+    system_prompt: Optional[str]     # ✅ New field for system prompt
     
 # -------------------
 # 3. Chat Node (Main LLM Node)