diff --git a/scripts/migrate-black.py b/scripts/migrate-black.py
index 4b29aebae36..a39c0e2f673 100755
--- a/scripts/migrate-black.py
+++ b/scripts/migrate-black.py
@@ -5,14 +5,15 @@
 import logging
 import os
 import sys
+from collections import abc
 from subprocess import check_output, run, Popen, PIPE
 
 
-def git(*args):
+def git(*args: abc.Iterable[str]) -> str:
     return check_output(["git"] + list(args)).decode("utf8").strip()
 
 
-def blackify(base_branch, black_command, logger):
+def blackify(base_branch: str, black_command: str, logger: logging.Logger) -> int:
     current_branch = git("branch", "--show-current")
 
     if not current_branch or base_branch == current_branch:
@@ -70,13 +71,16 @@ def blackify(base_branch, black_command, logger):
             ],
             stdin=git_diff.stdout,
         )
-        git_diff.stdout.close()
+        if git_diff.stdout is not None:
+            git_diff.stdout.close()
         git_apply.communicate()
         git("commit", "--allow-empty", "-aqC", commit)
 
     for commit in commits:
         git("branch", "-qD", "%s-black" % commit)
 
+    return 0
+
 
 if __name__ == "__main__":
     import argparse