use pythons contextlib instead of a backport package
diff --git a/parametrize_from_file/schema.py b/parametrize_from_file/schema.py
index 05c9092..869a621 100644
--- a/parametrize_from_file/schema.py
+++ b/parametrize_from_file/schema.py
@@ -2,7 +2,7 @@ import pytest, re
 from .errors import ConfigError
 from unittest.mock import MagicMock
 from more_itertools import always_iterable
-from contextlib2 import nullcontext
+from contextlib import nullcontext
 
 def cast(**funcs):
     """