Update onnx export config

Signed-off-by: Jael Gu <mengjia.gu@zilliz.com>

auto_transformers.py

@@ -142,6 +142,7 @@ class AutoTransformers(NNOperator):
     @property
     def onnx_config(self):
         from transformers.onnx.features import FeaturesManager
+        try:
             model_kind, model_onnx_config = FeaturesManager.check_supported_model_or_raise(
                 self._model, feature='default')
             old_config = model_onnx_config(self.model_config)
@@ -149,6 +150,14 @@ class AutoTransformers(NNOperator):
                 'inputs': dict(old_config.inputs),
                 'outputs': {'last_hidden_state': old_config.outputs['last_hidden_state']}
             }
+        except Exception:
+            input_dict = {}
+            for k in self.tokenizer.model_input_names:
+                input_dict[k] = {0: 'batch_size', 1: 'sequence_length'}
+            onnx_config = {
+                'inputs': input_dict,
+                'outputs': {'last_hidden_state': {0: 'batch_size', 1: 'sequence_length'}}
+            }
         return onnx_config
 
     def post_proc(self, token_embeddings, inputs):