[Bug]: Internal Server Error when use max_tokens=null

[cfytrok]

Your current environment

"version": "0.8.5.post1"

🐛 Describe the bug

vllm completions api does not support max_tokens=null, although openai does. https://platform.openai.com/docs/api-reference/completions/create

Request:
http://vllm.host/v1/completions

{
"model":"Qwen/Qwen2.5-Coder-7B-Instruct-AWQ",
"prompt":"test",
"temperature": 0, 
"max_tokens": null
}

Response:
Internal Server Error

logs

``` AssertionError

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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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assert request.max_tokens is not None
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File "/usr/local/lib/python3.12/dist-packages/vllm/entrypoints/openai/serving_completion.py", line 419, in request_output_to_completion_response
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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response = self.request_output_to_completion_response(
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File "/usr/local/lib/python3.12/dist-packages/vllm/entrypoints/openai/serving_completion.py", line 219, in create_completion
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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generator = await handler.create_completion(request, raw_request)
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File "/usr/local/lib/python3.12/dist-packages/vllm/entrypoints/openai/api_server.py", line 498, in create_completion
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^^^^^^^^^^^^^^^^^^^^^^^^^^^
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return await func(*args, **kwargs)
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File "/usr/local/lib/python3.12/dist-packages/vllm/entrypoints/utils.py", line 85, in wrapper
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^^^^^^^^^^^^^^^^^^^^^
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return handler_task.result()
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File "/usr/local/lib/python3.12/dist-packages/vllm/entrypoints/utils.py", line 63, in wrapper
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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return await dependant.call(**values)
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File "/usr/local/lib/python3.12/dist-packages/fastapi/routing.py", line 212, in run_endpoint_function
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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raw_response = await run_endpoint_function(
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File "/usr/local/lib/python3.12/dist-packages/fastapi/routing.py", line 301, in app
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^^^^^^^^^^^^^^^^
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response = await f(request)
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File "/usr/local/lib/python3.12/dist-packages/starlette/routing.py", line 73, in app
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await app(scope, receive, sender)
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File "/usr/local/lib/python3.12/dist-packages/starlette/_exception_handler.py", line 42, in wrapped_app
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raise exc
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File "/usr/local/lib/python3.12/dist-packages/starlette/_exception_handler.py", line 53, in wrapped_app
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await wrap_app_handling_exceptions(app, request)(scope, receive, send)
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File "/usr/local/lib/python3.12/dist-packages/starlette/routing.py", line 76, in app
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await self.app(scope, receive, send)
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File "/usr/local/lib/python3.12/dist-packages/starlette/routing.py", line 288, in handle
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await route.handle(scope, receive, send)
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File "/usr/local/lib/python3.12/dist-packages/starlette/routing.py", line 734, in app
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await self.middleware_stack(scope, receive, send)
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File "/usr/local/lib/python3.12/dist-packages/starlette/routing.py", line 714, in call
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await app(scope, receive, sender)
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File "/usr/local/lib/python3.12/dist-packages/starlette/_exception_handler.py", line 42, in wrapped_app
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raise exc
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File "/usr/local/lib/python3.12/dist-packages/starlette/_exception_handler.py", line 53, in wrapped_app
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await wrap_app_handling_exceptions(self.app, conn)(scope, receive, send)
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File "/usr/local/lib/python3.12/dist-packages/starlette/middleware/exceptions.py", line 62, in call
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await self.app(scope, receive, send_wrapper)
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File "/usr/local/lib/python3.12/dist-packages/prometheus_fastapi_instrumentator/middleware.py", line 175, in call
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raise exc
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File "/usr/local/lib/python3.12/dist-packages/prometheus_fastapi_instrumentator/middleware.py", line 177, in call
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await self.app(scope, receive, send)
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File "/usr/local/lib/python3.12/dist-packages/starlette/middleware/cors.py", line 85, in call
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await self.app(scope, receive, _send)
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File "/usr/local/lib/python3.12/dist-packages/starlette/middleware/errors.py", line 165, in call
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raise exc
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File "/usr/local/lib/python3.12/dist-packages/starlette/middleware/errors.py", line 187, in call
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await self.middleware_stack(scope, receive, send)
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File "/usr/local/lib/python3.12/dist-packages/starlette/applications.py", line 112, in call
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await super().call(scope, receive, send)
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File "/usr/local/lib/python3.12/dist-packages/fastapi/applications.py", line 1054, in call
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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return await self.app(scope, receive, send)
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File "/usr/local/lib/python3.12/dist-packages/uvicorn/middleware/proxy_headers.py", line 60, in call
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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result = await app( # type: ignore[func-returns-value]
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File "/usr/local/lib/python3.12/dist-packages/uvicorn/protocols/http/httptools_impl.py", line 409, in run_asgi
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Traceback (most recent call last):

</details>

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[princepride]

Maybe you should use None instead of null