[Bugfix] Validate custom logits processor xargs for online serving (#27560)

Signed-off-by: Isotr0py <mozf@mail2.sysu.edu.cn>

examples/offline_inference/logits_processor/custom_req.py

@@ -76,6 +76,14 @@ class WrappedPerReqLogitsProcessor(AdapterLogitsProcessor):
     """Example of wrapping a fake request-level logit processor to create a
     batch-level logits processor"""
 
+    @classmethod
+    def validate_params(cls, params: SamplingParams):
+        target_token: Any | None = params.extra_args and params.extra_args.get(
+            "target_token"
+        )
+        if target_token is not None and not isinstance(target_token, int):
+            raise ValueError(f"target_token value {target_token} is not int")
+
     def is_argmax_invariant(self) -> bool:
         return False
 
@@ -101,13 +109,6 @@ class WrappedPerReqLogitsProcessor(AdapterLogitsProcessor):
         )
         if target_token is None:
             return None
-        if not isinstance(target_token, int):
-            logger.warning(
-                "target_token value %s is not int; not applying logits"
-                " processor to request.",
-                target_token,
-            )
-            return None
         return DummyPerReqLogitsProcessor(target_token)