added missing imports

modeling_lsg_bert.py

@@ -14,12 +14,20 @@ from transformers.models.bert.modeling_bert import (
     BertLayer,
     BertPooler,
     BertSelfOutput,
+    BertAttention,
+    BertOnlyNSPHead,
+    BertOnlyMLMHead,
+    BertPreTrainingHeads,
+    BertForPreTraining,
+    BertLMHeadModel,
 )
 import torch
 import torch.nn as nn
+from transformers.modeling_outputs import BaseModelOutputWithPastAndCrossAttentions
 from transformers.models.bert.configuration_bert import BertConfig
 import math
 import sys
+from typing import Optional, Tuple, Union
 
 import logging
 logger = logging.getLogger(__name__)