Fix a bug raised by issue 3372. (#3399)

* Fix a bug raised by issue 3372.

corner case: the input tensor may also be the input tensor of the whole
model.

nni/common/graph_utils.py

@@ -441,7 +441,11 @@ class TorchModuleGraph(TorchGraph):
         input_tensors = list(list_construct_cpp.inputs())
         for _tensor in input_tensors:
             debug_name = _tensor.debugName()
-            input_order.append(self.output_to_node[debug_name].unique_name)
+            if debug_name in self.output_to_node:
+                input_order.append(self.output_to_node[debug_name].unique_name)
+            else:
+                # the input tensor may be the input tensor of the whole model
+                input_order.append(None)
         cat_info['in_order'] = input_order
         input_shapes = [t.type().sizes() for t in input_tensors]
         cat_info['in_shape'] = input_shapes