fix: drop past-memory directive and placeholder from agent prompts when memory is empty (#572)

tradingagents/agents/researchers/bear_researcher.py

@@ -19,6 +19,17 @@ def create_bear_researcher(llm, memory):
         for i, rec in enumerate(past_memories, 1):
             past_memory_str += rec["recommendation"] + "\n\n"
 
+        memory_section = (
+            f"Reflections from similar situations and lessons learned: {past_memory_str.strip()}\n"
+            if past_memories
+            else ""
+        )
+        memory_instruction = (
+            " You must also address reflections and learn from lessons and mistakes you made in the past."
+            if past_memories
+            else ""
+        )
+
         prompt = f"""You are a Bear Analyst making the case against investing in the stock. Your goal is to present a well-reasoned argument emphasizing risks, challenges, and negative indicators. Leverage the provided research and data to highlight potential downsides and counter bullish arguments effectively.
 
 Key points to focus on:
@@ -37,8 +48,7 @@ Latest world affairs news: {news_report}
 Company fundamentals report: {fundamentals_report}
 Conversation history of the debate: {history}
 Last bull argument: {current_response}
-Reflections from similar situations and lessons learned: {past_memory_str}
-Use this information to deliver a compelling bear argument, refute the bull's claims, and engage in a dynamic debate that demonstrates the risks and weaknesses of investing in the stock. You must also address reflections and learn from lessons and mistakes you made in the past.
+{memory_section}Use this information to deliver a compelling bear argument, refute the bull's claims, and engage in a dynamic debate that demonstrates the risks and weaknesses of investing in the stock.{memory_instruction}
 """
 
         response = llm.invoke(prompt)