groq: handle null queue_time (#20839)

libs/partners/groq/langchain_groq/chat_models.py

@@ -469,7 +469,7 @@ def _combine_llm_outputs(self, llm_outputs: List[Optional[dict]]) -> dict:
             token_usage = output["token_usage"]
             if token_usage is not None:
                 for k, v in token_usage.items():
-                    if k in overall_token_usage:
+                    if k in overall_token_usage and v is not None:
                         overall_token_usage[k] += v
                     else:
                         overall_token_usage[k] = v