[REGRESSION] uninitialized value $address in git send-email

Hi,

Recently when I was submitting doc fixes to linux-doc mailing list [1] using git-send-email(1), I got perl-related error:

``` Use of uninitialized value $address in sprintf at /home/bagas/.app/git/dist/v2.42.0/libexec/git-core/git-send-email line 1172. error: unable to extract a valid address from: ```

My linux.git clone has sendemail-validate hook which uses patatt (from b4 package). The hook is:

``` #!/bin/sh # installed by patatt install-hook patatt sign --hook "${1}" ```

This issue occurs on Git v2.41.0 but not in v2.40.0. Bisecting, the culprit is commit a8022c5f7b67 (send-email: expose header information to git-send-email's sendemail-validate hook, 2023-04-19). Emily's earlier report [2] also points to the same culprit, but with different bug.

I triggered this issue on patch series with cover letter. To reproduce:

1. Clone git.git repo, then branch off:

   ```
   $ git clone https://github.com/git/git.git && cd git
   $ git checkout -b test
   ```

2. Make two dummy signed-off commits:

   ```
   $ echo test > test && git add test && git commit -s -m "test"
   $ echo "test test" >> test && git commit -a -s -m "test test"
   ```

3. Generate patch series:

   ```
   $ mkdir /tmp/test
   $ git format-patch -o /tmp/test --cover-letter main
   ```

4. Send the series to dummy address:

   ```
   $ git send-email --to="pi <pi@pi>" /tmp/test/*.patch
   ```

git-send-email(1) trips on the cover letter since there is no recipient addresses detected. It also errored out on patches without Signed-off-by trailer. When the command should have been succeeded, I expected that it asked me whether to send each patch or not.

My system runs Debian testing (trixie/sid) with perl 5.36.0.

Thanks.

[1]: https://lore.kernel.org/linux-doc/20230918093240.29824-1-bagasdotme@gmail.com/ [2]: https://lore.kernel.org/git/CAJoAoZ=GGgjGOeaeo6RFBO7=6msdRf-Ze6XcnL04K5ugupLUJA@mail.gmail.com/