Fix typing for None valued variables (#37004)

Fix typing for None-able variables

src/transformers/model_debugging_utils.py

@@ -19,6 +19,7 @@ import json
 import os
 import re
 from contextlib import contextmanager
+from typing import Optional
 
 from transformers.utils.import_utils import export
 
@@ -284,7 +285,7 @@ def model_addition_debugger(cls):
 
 @export(backends=("torch",))
 @contextmanager
-def model_addition_debugger_context(model, debug_path: str = None):
+def model_addition_debugger_context(model, debug_path: Optional[str] = None):
     """
     # Model addition debugger - context manager for model adders
     This context manager is a power user tool intended for model adders.