[BugFix] Fix EPLB fail for MoeFP4 model with Marlin backend (#33262)

Signed-off-by: ilmarkov <markovilya197@gmail.com>

vllm/model_executor/utils.py

@@ -44,7 +44,9 @@ def set_weight_attrs(
         setattr(weight, key, value)
 
 
-def replace_parameter(layer: torch.nn.Module, param_name: str, new_data: torch.Tensor):
+def replace_parameter(
+    layer: torch.nn.Module, param_name: str, new_data: torch.Tensor | None
+):
     """
     Replace a parameter of a layer while maintaining the ability to reload the weight.
     Called within implementations of the `process_weights_after_loading` method.
@@ -54,9 +56,15 @@ def replace_parameter(layer: torch.nn.Module, param_name: str, new_data: torch.T
     Args:
         layer: Layer containing parameter to replace
         param_name: Name of parameter to replace
-        new_data: New data of the new parameter
+        new_data: New data of the new parameter, or None to set the parameter to None
     """
     # should not be used on a tied/shared param
+
+    # If new_data is None, set the parameter to None
+    if new_data is None:
+        setattr(layer, param_name, None)
+        return
+
     if isinstance(new_data, torch.nn.Parameter):
         new_data = new_data.data
     new_param = torch.nn.Parameter(new_data, requires_grad=False)