[Bugfix] use served_model_name for multimodal error message (#41003)

Signed-off-by: Moritz Sanft <58110325+msanft@users.noreply.github.com>

tests/multimodal/test_registry.py

@@ -5,6 +5,8 @@ Unit tests for MultiModalRegistry.supports_multimodal_inputs and
 Qwen2.5-VL visual component loading behavior.
 """
 
+from types import SimpleNamespace
+
 import pytest
 
 from vllm.multimodal import MULTIMODAL_REGISTRY
@@ -32,3 +34,17 @@ def test_supports_multimodal_inputs(model_id, limit_mm_per_prompt, expected):
         limit_mm_per_prompt=limit_mm_per_prompt,
     )
     assert MULTIMODAL_REGISTRY.supports_multimodal_inputs(ctx.model_config) is expected
+
+
+def test_create_processor_error_uses_served_model_name():
+    model_config = SimpleNamespace(
+        is_multimodal_model=False,
+        model="/path/to/model/weights",
+        served_model_name="friendly-model-name",
+    )
+
+    with pytest.raises(
+        ValueError,
+        match="friendly-model-name is not a multimodal model",
+    ):
+        MULTIMODAL_REGISTRY.create_processor(model_config)

vllm/multimodal/registry.py

@@ -207,7 +207,8 @@ class MultiModalRegistry:
         Create a multi-modal processor for a specific model and tokenizer.
         """
         if not model_config.is_multimodal_model:
-            raise ValueError(f"{model_config.model} is not a multimodal model")
+            model_name = model_config.served_model_name or model_config.model
+            raise ValueError(f"{model_name} is not a multimodal model")
 
         model_cls = self._get_model_cls(model_config)
         factories = model_cls._processor_factory