[Config Refactor] sentinel default precedence (#3078)

Signed-off-by: lishunyang <lishunyang12@163.com>
Signed-off-by: xiaohajiayou <923390377@qq.com>
Co-authored-by: lishunyang <lishunyang12@163.com>

tests/entrypoints/test_omni_entrypoints.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import argparse
 import queue
 from collections.abc import Callable
 from types import SimpleNamespace
@@ -166,6 +167,31 @@ def _patch_engine(monkeypatch: pytest.MonkeyPatch, engine: FakeAsyncOmniEngine)
     monkeypatch.setattr("vllm_omni.entrypoints.omni_base.omni_snapshot_download", lambda model: model)
 
 
+def test_from_cli_args_only_nulls_untyped_override_fields(monkeypatch: pytest.MonkeyPatch):
+    from vllm_omni.entrypoints.omni import Omni
+
+    captured: dict[str, Any] = {}
+
+    def fake_engine(*args: Any, **kwargs: Any) -> FakeAsyncOmniEngine:
+        captured.update(kwargs)
+        return FakeAsyncOmniEngine()
+
+    monkeypatch.setattr("vllm_omni.entrypoints.omni_base.AsyncOmniEngine", fake_engine)
+    monkeypatch.setattr("vllm_omni.entrypoints.omni_base.omni_snapshot_download", lambda model: model)
+    monkeypatch.setattr("sys.argv", ["prog"])
+
+    parser = argparse.ArgumentParser()
+    parser.add_argument("--gpu-memory-utilization", type=float, default=0.9)
+    parser.add_argument("--hsdp-shard-size", type=int, default=-1)
+    args = parser.parse_args([])
+    args.model = "fake-model"
+
+    Omni.from_cli_args(args, parser=parser)
+
+    assert captured["gpu_memory_utilization"] is None
+    assert captured["hsdp_shard_size"] == -1
+
+
 def _make_base():
     from vllm_omni.entrypoints.omni_base import OmniBase