Before patch, running 'arc patch' could fail.
```
% arc patch
ing D37961
Exception
preg_match(): Passing null to parameter #2 ($subject) of type string is deprecated
(Run with `--trace` for a full exception trace.)
```
With `--trace`:
```
% arc patch --trace D37961
ARGV /usr/local/bin/arc patch --trace D37961
PCNTL Unable to install signal handler, pcntl_signal() unavailable. Continuing without signal handling.
>>> [0] (+0) <exec> $ /usr/local/bin/php -f /usr/local/lib/php/arcanist/scripts/arcanist.php -- patch --trace D37961
ARGV /usr/local/lib/php/arcanist/scripts/arcanist.php patch --trace D37961
LOAD Loaded "arcanist" from "/usr/local/lib/php/arcanist/src".
Config: Reading user configuration file "/home/jrm/.arcrc"...
Config: Did not find system configuration at "/etc/arcconfig".
Working Copy: Reading .arcconfig from "/usr/ports/.arcconfig".
Working Copy: Path "/usr/ports/devel/arcanist-lib" is part of `git` working copy "/usr/ports".
Working Copy: Project root is at "/usr/ports".
Config: Did not find local configuration at "/usr/ports/.git/arc/config".
>>> [0] (+0) <http> https://reviews.freebsd.org/api/differential.querydiffs
<<< [0] (+636) <http> 636,457 us
>>> [1] (+637) <http> https://reviews.freebsd.org/api/user.whoami
<<< [1] (+692) <http> 55,693 us
>>> [2] (+693) <http> https://reviews.freebsd.org/api/differential.querydiffs
<<< [2] (+938) <http> 244,954 us
>>> [3] (+947) <http> https://reviews.freebsd.org/api/repository.query
<<< [3] (+1,003) <http> 56,653 us
>>> [4] (+1,006) <exec> $ git --version
<<< [4] (+1,016) <exec> 9,685 us
>>> [5] (+1,016) <exec> $ git status --porcelain=2 -z
<<< [5] (+1,531) <exec> 514,642 us
[2023-01-06 16:45:12] EXCEPTION: (RuntimeException) preg_match(): Passing null to parameter #2 ($subject) of type string is deprecated at [<arcanist>/src/error/PhutilErrorHandler.php:261]
arcanist()
#0 PhutilErrorHandler::handleError(integer, string, string, integer)
#1 preg_match(string, NULL, NULL) called at [<arcanist>/src/repository/api/ArcanistGitAPI.php:603]
#2 ArcanistGitAPI::getCanonicalRevisionName(NULL) called at [<arcanist>/src/repository/api/ArcanistGitAPI.php:1146]
#3 ArcanistGitAPI::hasLocalCommit(NULL) called at [<arcanist>/src/workflow/ArcanistPatchWorkflow.php:433]
#4 ArcanistPatchWorkflow::run() called at [<arcanist>/src/workflow/ArcanistPatchWorkflow.php:398]
#5 ArcanistPatchWorkflow::run() called at [<arcanist>/scripts/arcanist.php:427]
<<< [0] (+1,563) <exec> 1,563,354 us
```