[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_init.py

@@ -77,6 +77,14 @@ class WrappedPerReqLogitsProcessor(AdapterLogitsProcessor):
     """Example of overriding the wrapper class `__init__()` in order to utilize
     info about the device type"""
 
+    @classmethod
+    def validate_params(cls, params: SamplingParams):
+        target_token = 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` has to be an integer, got {target_token}."
+            )
+
     def __init__(
         self, vllm_config: VllmConfig, device: torch.device, is_pin_memory: bool
     ):
@@ -113,13 +121,6 @@ class WrappedPerReqLogitsProcessor(AdapterLogitsProcessor):
             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)