check for empty messages

Author: alexander-alderman-webb

sentry_sdk/integrations/langgraph.py

@@ -351,6 +351,9 @@ def _set_usage_data(span, messages):
 
 def _set_response_model_name(span, messages):
     # type: (sentry_sdk.tracing.Span, Any) -> None
+    if len(messages) == 0:
+        return
+
     last_message = messages[-1]
     response_metadata = last_message.get("response_metadata")
     if response_metadata is None: