Update agent.py

agent.py

@@ -1133,10 +1133,13 @@ def build_graph(vector_store, provider: str, model_config: dict) -> StateGraph:
     builder.set_entry_point("retriever")
     builder.add_edge("retriever", "assistant")
     builder.add_edge("assistant", "call_llm")
+    builder.add_node("end", lambda state: state)  # Add a terminal node
+    
     builder.add_conditional_edges("call_llm", should_call_tool, {
         "call_tool": "call_tool",
-        "end": None
+        "end": "end"  
     })
+
     builder.add_edge("call_tool", "call_llm")
 
     return builder.compile()