force git to allow empty commit message. it's just a hacky joke with experiment. use it on your own risk in production

allow-empty-message.patch

diff --git a/builtin/commit.c b/builtin/commit.c
index 2f45968222..25e26a2f70 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -125,7 +125,7 @@ static int all, also, interactive, patch_interactive, only, amend, signoff;
 static int edit_flag = -1; /* unspecified */
 static int quiet, verbose, no_verify, allow_empty, dry_run, renew_authorship;
 static int config_commit_verbose = -1; /* unspecified */
-static int no_post_rewrite, allow_empty_message, pathspec_file_nul;
+static int no_post_rewrite, allow_empty_message = 1, pathspec_file_nul;
 static const char *untracked_files_arg, *force_date, *ignore_submodule_arg, *ignored_arg;
 static const char *sign_commit, *pathspec_from_file;
 static struct strvec trailer_args = STRVEC_INIT;

home.nix

{
  programs.git = {
    enable = true;
    package = pkgs.git.overrideAttrs (p: {
      patches = p.patches ++ [ ./allow-empty-message.patch ];
      preInstallCheck =
        p.preInstallCheck
        + ''
          disable_test t3404-rebase-interactive
          disable_test t3405-rebase-malformed
          disable_test t6429-merge-sequence-rename-caching
          disable_test t7500-commit-template-squash-signoff
          disable_test t7501-commit-basic-functionality
          disable_test t7502-commit-porcelain
          disable_test t7507-commit-verbose
          disable_test t7508-status
        '';
    });
  };
}