[Mypy] Part 3 fix typing for nested directories for most of directory (#4161)

vllm/entrypoints/openai/api_server.py

@@ -18,6 +18,7 @@ from vllm.engine.arg_utils import AsyncEngineArgs
 from vllm.engine.async_llm_engine import AsyncLLMEngine
 from vllm.entrypoints.openai.cli_args import make_arg_parser
 from vllm.entrypoints.openai.protocol import (ChatCompletionRequest,
+                                              ChatCompletionResponse,
                                               CompletionRequest, ErrorResponse)
 from vllm.entrypoints.openai.serving_chat import OpenAIServingChat
 from vllm.entrypoints.openai.serving_completion import OpenAIServingCompletion
@@ -26,8 +27,8 @@ from vllm.usage.usage_lib import UsageContext
 
 TIMEOUT_KEEP_ALIVE = 5  # seconds
 
-openai_serving_chat: OpenAIServingChat = None
-openai_serving_completion: OpenAIServingCompletion = None
+openai_serving_chat: OpenAIServingChat
+openai_serving_completion: OpenAIServingCompletion
 logger = init_logger(__name__)
 
 
@@ -95,6 +96,7 @@ async def create_chat_completion(request: ChatCompletionRequest,
         return StreamingResponse(content=generator,
                                  media_type="text/event-stream")
     else:
+        assert isinstance(generator, ChatCompletionResponse)
         return JSONResponse(content=generator.model_dump())