pre-commit-hooks: end-of-file-fixer fails against a ".git/MERGE_MSG" file

I’m running git merge --no-ff release-7.1.2 -m "Merge branch 'release-7.1.2' into master" and it fails because it’s incorrectly checking files inside the .git directory:

Fix End of Files.........................................................Failed
hookid: end-of-file-fixer

Fixing .git/MERGE_MSG

pre-commit 1.11.1
git version 2.19.0
macOS 10.14 (18A391)