[MRV2] Validate MRV2 entrypoint logits processors (#57728)

Signed-off-by: Taneem Ibrahim <taneem.ibrahim@gmail.com>

vllm/v1/engine/input_processor.py

@@ -97,6 +97,9 @@ class InputProcessor:
         params validator for the active model runner."""
         custom_logitsprocs = self.model_config.logits_processors
         if self.vllm_config.use_v2_model_runner:
+            if self.model_config.runner_type == "pooling" and not custom_logitsprocs:
+                return lambda _: None
+
             from vllm.v1.worker.gpu.sample.logits_processor import (
                 build_custom_logits_processors_params_validator,
             )

vllm/v1/worker/gpu/sample/logits_processor/loader.py

@@ -196,10 +196,10 @@ def build_custom_logits_processors_params_validator(
         RuntimeError: if an FQCN fails to import.
 
     """
-    if not custom_logitsprocs:
-        return lambda _: None
+    classes = _cached_load_v2_logitsprocs(tuple(custom_logitsprocs or ()))
 
-    classes = _cached_load_v2_logitsprocs(tuple(custom_logitsprocs))
+    if not classes:
+        return lambda _: None
 
     def validate_params(sampling_params: "SamplingParams") -> None:
         for cls in classes: