fix(cookbook): also guard message.content=None for tool-call responses

cookbook/litellm_router/load_test_proxy.py

@@ -99,9 +99,10 @@ def make_openai_completion(question):
         # Log the request details
         if not response.choices or response.choices[0].message is None:
             raise ValueError("LLM returned empty or filtered response")
+        content_preview = (response.choices[0].message.content or "")[:10]
         with open("request_log.txt", "a") as log_file:
             log_file.write(
-                f"Question: {question[:100]}\nResponse ID:{response.id} Content:{response.choices[0].message.content[:10]}\nTime: {end_time - start_time:.2f} seconds\n\n"
+                f"Question: {question[:100]}\nResponse ID:{response.id} Content:{content_preview}\nTime: {end_time - start_time:.2f} seconds\n\n"
             )
 
         return response