Fixups: We use our own nullcontext() function

Author: rickprice

git/cmd.py

@@ -809,7 +809,7 @@ def execute(self, command,
                 cmd_not_found_exception = FileNotFoundError  # NOQA # exists, flake8 unknown @UndefinedVariable
             else:
                 cmd_not_found_exception = OSError
-            patch_caller_env = contextlib.nullcontext()
+            patch_caller_env = nullcontext()
         # end handle
 
         stdout_sink = (PIPE