diff --git a/openllm-python/src/_openllm_tiny/_service.py b/openllm-python/src/_openllm_tiny/_service.py
index cb08689a..2f88bff3 100644
--- a/openllm-python/src/_openllm_tiny/_service.py
+++ b/openllm-python/src/_openllm_tiny/_service.py
@@ -72,7 +72,11 @@ class LLMService:
     request_id: t.Optional[str] = None,
     llm_config: t.Dict[str, t.Any] = pydantic.Field(default=LLMConfig, description='LLM Config'),
   ) -> core.GenerationOutput:
-    llm_config.update(stop=stop, stop_token_ids=stop_token_ids)
+    if stop:
+      llm_config.update(stop=stop)
+    if stop_token_ids:
+      llm_config.update(stop_token_ids=stop_token_ids)
+
     return await self.llm.generate(
       prompt=prompt, prompt_token_ids=prompt_token_ids, request_id=request_id, **llm_config
     )
@@ -87,7 +91,10 @@ class LLMService:
     request_id: t.Optional[str] = None,
     llm_config: t.Dict[str, t.Any] = pydantic.Field(default=LLMConfig, description='LLM Config'),
   ) -> t.AsyncGenerator[str, None]:
-    llm_config.update(stop=stop, stop_token_ids=stop_token_ids)
+    if stop:
+      llm_config.update(stop=stop)
+    if stop_token_ids:
+      llm_config.update(stop_token_ids=stop_token_ids)
 
     _config = LLMConfig.model_construct_env(**core.utils.dict_filter_none(llm_config))
     previous_texts = [''] * _config['n']