openai[patch], standard-tests[patch]: don't pass in falsey stop vals (#23153)

adds an image input test to standard-tests as well

libs/partners/openai/langchain_openai/chat_models/base.py

@@ -443,11 +443,12 @@ class BaseChatOpenAI(BaseChatModel):
             "stream": self.streaming,
             "n": self.n,
             "temperature": self.temperature,
-            "stop": self.stop,
             **self.model_kwargs,
         }
         if self.max_tokens is not None:
             params["max_tokens"] = self.max_tokens
+        if self.stop:
+            params["stop"] = self.stop
         return params
 
     def _combine_llm_outputs(self, llm_outputs: List[Optional[dict]]) -> dict: