Add Optional to remaining types (#37808)

More Optional typing

Signed-off-by: cyy <cyyever@outlook.com>

tests/extended/test_trainer_ext.py

@@ -17,6 +17,7 @@ import os
 import re
 import sys
 from pathlib import Path
+from typing import Optional
 from unittest.mock import patch
 
 from parameterized import parameterized
@@ -270,13 +271,13 @@ class TestTrainerExt(TestCasePlus):
         learning_rate: float = 3e-3,
         optim: str = "adafactor",
         distributed: bool = False,
-        extra_args_str: str = None,
+        extra_args_str: Optional[str] = None,
         eval_steps: int = 0,
         predict_with_generate: bool = True,
         do_train: bool = True,
         do_eval: bool = True,
         do_predict: bool = True,
-        n_gpus_to_use: int = None,
+        n_gpus_to_use: Optional[int] = None,
     ):
         data_dir = self.test_file_dir / "../fixtures/tests_samples/wmt_en_ro"
         output_dir = self.get_auto_remove_tmp_dir()