[Bugfix] fix custom op test (#25429)

Signed-off-by: Luka Govedič <lgovedic@redhat.com>

tests/model_executor/test_enabled_custom_ops.py

 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+from typing import Optional
 
 import pytest
 import torch
@@ -34,15 +35,15 @@ class Relu3(ReLUSquaredActivation):
     [
         # Default values based on compile level
         # - All by default (no Inductor compilation)
-        ("", 0, False, [True] * 4, True),
-        ("", 1, True, [True] * 4, True),
-        ("", 2, False, [True] * 4, True),
+        (None, 0, False, [True] * 4, True),
+        (None, 1, True, [True] * 4, True),
+        (None, 2, False, [True] * 4, True),
         # - None by default (with Inductor)
-        ("", 3, True, [False] * 4, False),
-        ("", 4, True, [False] * 4, False),
+        (None, 3, True, [False] * 4, False),
+        (None, 4, True, [False] * 4, False),
         # - All by default (without Inductor)
-        ("", 3, False, [True] * 4, True),
-        ("", 4, False, [True] * 4, True),
+        (None, 3, False, [True] * 4, True),
+        (None, 4, False, [True] * 4, True),
         # Explicitly enabling/disabling
         #
         # Default: all
@@ -54,7 +55,7 @@ class Relu3(ReLUSquaredActivation):
         # All but SiluAndMul
         ("all,-silu_and_mul", 2, True, [1, 0, 1, 1], True),
         # All but ReLU3 (even if ReLU2 is on)
-        ("-relu3,relu2", 3, False, [1, 1, 1, 0], True),
+        ("-relu3,+relu2", 3, False, [1, 1, 1, 0], True),
         # RMSNorm and SiluAndMul
         ("none,-relu3,+rms_norm,+silu_and_mul", 4, False, [1, 1, 0, 0], False),
         # All but RMSNorm
@@ -67,12 +68,13 @@ class Relu3(ReLUSquaredActivation):
         # All but RMSNorm
         ("all,-rms_norm", 4, True, [0, 1, 1, 1], True),
     ])
-def test_enabled_ops(env: str, torch_level: int, use_inductor: bool,
+def test_enabled_ops(env: Optional[str], torch_level: int, use_inductor: bool,
                      ops_enabled: list[int], default_on: bool):
+    custom_ops = env.split(',') if env else []
     vllm_config = VllmConfig(
         compilation_config=CompilationConfig(use_inductor=bool(use_inductor),
                                              level=torch_level,
-                                             custom_ops=env.split(",")))
+                                             custom_ops=custom_ops))
     with set_current_vllm_config(vllm_config):
         assert CustomOp.default_on() == default_on