fix: st backwards compatibility

custom_st.py

@@ -2,7 +2,7 @@ import base64
 import json
 import os
 from io import BytesIO
-from typing import Any, Dict, List, Optional, Tuple, Union
+from typing import Any, Dict, List, Literal, Optional, Union
 
 import requests
 import torch
@@ -43,8 +43,15 @@ class Transformer(nn.Module):
         cache_dir: Optional[str] = None,
         do_lower_case: bool = False,
         tokenizer_name_or_path: str = None,
+        backend: Literal['torch', 'onnx', 'openvino'] = 'torch',
+        **_,
     ) -> None:
         super(Transformer, self).__init__()
+        if backend != 'torch':
+            raise ValueError(
+                f'Backend \'{backend}\' is not supported, please use \'torch\' instead'
+            )
+
         self.config_keys = ["max_seq_length", "do_lower_case"]
         self.do_lower_case = do_lower_case
         if model_args is None: