Add missing import (#8444)

* Add missing import

* Fix dummy objects

src/transformers/__init__.py

@@ -651,6 +651,7 @@ if is_tf_available():
         TF_MODEL_FOR_CAUSAL_LM_MAPPING,
         TF_MODEL_FOR_MASKED_LM_MAPPING,
         TF_MODEL_FOR_MULTIPLE_CHOICE_MAPPING,
+        TF_MODEL_FOR_NEXT_SENTENCE_PREDICTION_MAPPING,
         TF_MODEL_FOR_PRETRAINING_MAPPING,
         TF_MODEL_FOR_QUESTION_ANSWERING_MAPPING,
         TF_MODEL_FOR_SEQ_TO_SEQ_CAUSAL_LM_MAPPING,

src/transformers/utils/dummy_tf_objects.py

@@ -101,6 +101,9 @@ TF_MODEL_FOR_MASKED_LM_MAPPING = None
 TF_MODEL_FOR_MULTIPLE_CHOICE_MAPPING = None
 
 
+TF_MODEL_FOR_NEXT_SENTENCE_PREDICTION_MAPPING = None
+
+
 TF_MODEL_FOR_PRETRAINING_MAPPING = None