[QNN] Guard get_parameter against node=None in LayerNormVisitor

Fixes AttributeError when aten.native_layer_norm has optional weight=None.
Both weight and bias are guarded to handle the None case gracefully.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: KevinUW114514

backends/qualcomm/builders/op_layer_norm.py

@@ -55,16 +55,22 @@ def define_node(
         axis_shape = [len(axis)]
 
         weight_node = self.get_node(node.args[2])
-        weight_tensor = get_parameter(weight_node, self.edge_program)
-        weight_tensor_wrapper = self.define_tensor(
-            weight_node,
-            node,
-            weight_tensor,
-            PyQnnManager.Qnn_TensorType_t.QNN_TENSOR_TYPE_STATIC,
-            nodes_to_wrappers,
-        )
-
-        layer_norm_input_tensors = [input_tensor_wrapper, weight_tensor_wrapper]
+        if weight_node is not None:
+            weight_tensor = get_parameter(weight_node, self.edge_program)
+            weight_tensor_wrapper = self.define_tensor(
+                weight_node,
+                node,
+                weight_tensor,
+                PyQnnManager.Qnn_TensorType_t.QNN_TENSOR_TYPE_STATIC,
+                nodes_to_wrappers,
+            )
+            layer_norm_input_tensors = [input_tensor_wrapper, weight_tensor_wrapper]
+        else:
+            warnings.warn(
+                "[QNN Delegate Op Builder]: LayerNorm weight is None, skipping",
+                stacklevel=1,
+            )
+            layer_norm_input_tensors = [input_tensor_wrapper]
 
         bias_node = self.get_node(node.args[3])
         if bias_node is not None:

backends/qualcomm/builders/utils.py

@@ -29,7 +29,9 @@ def is_parameter(
 
 def get_parameter(
     node: torch.fx.Node, edge_program: torch.export.ExportedProgram
-) -> torch.Tensor:
+) -> Optional[torch.Tensor]:
+    if node is None:
+        return None
     param = None
     if is_param(edge_program, node):
         param = get_param(edge_program, node)