fix(caldav): harden null handling of iMip scheduling method

[st3iny]

• Ref fix(caldav): convert iMip recipient name to a string #36898 (comment)

Summary

The schedule() method of the iMip plugin poorly handles various null values. I hardened it a bit to prevent further breakage in the future.

This PR can be tested using the following patch:

diff --git a/apps/dav/lib/CalDAV/Schedule/IMipPlugin.php b/apps/dav/lib/CalDAV/Schedule/IMipPlugin.php
index ca79205c09f..8c4507b0870 100644
--- a/apps/dav/lib/CalDAV/Schedule/IMipPlugin.php+++ b/apps/dav/lib/CalDAV/Schedule/IMipPlugin.php@@ -209,6 +209,9 @@ class IMipPlugin extends SabreIMipPlugin {
$senderName = $senderName->getValue() ?? null;
}
+ $senderName = null;+ $this->userId = null;+
// Try to get the sender name from the current user id if available.
if ($this->userId !== null && ($senderName === null || empty(trim($senderName)))) {
$senderName = $this->userManager->getDisplayName($this->userId);

TODO

• Trigger backports when backports of Include more information in iMIP email and show diff information on updating an event #35743 were merged

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[nickvergessen]

./autotest.sh sqlite apps/dav/tests/unit/CalDAV/Schedule/
Using PHP executable /usr/bin/php
Using database oc_autotest
Setup environment for sqlite testing on local storage ...
0 Pfade vom Index aktualisiert
Installing ....
Nextcloud was successfully installed
Testing with sqlite ...
No coverage
/home/nickv/Tools/vendor/bin/phpunit --configuration phpunit-autotest.xml --log-junit autotest-results-sqlite.xml ../apps/dav/tests/unit/CalDAV/Schedule/ PHPUnit 9.6.0 by Sebastian Bergmann and contributors.
Runtime: PHP 8.0.28
Configuration: phpunit-autotest.xml
.............................. 30 / 30 (100%)
Time: 00:00.085, Memory: 34.00 MB
OK (30 tests, 128 assertions)

Could we extend the tests?

[st3iny]

/rebase

[kesselb]

/backport to stable25

[backportbot-nextcloud]

The backport to stable25 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable25
git pull origin stable25
# Create the new backport branch
git checkout -b fix/foo-stable25
# Cherry pick the change from the commit sha1 of the change against the default branch# This might cause conflicts. Resolve them.
git cherry-pick abc123
# Push the cherry pick commit to the remote repository and open a pull request
git push origin fix/foo-stable25

More info at https://docs.nextcloud.com/server/latest/developer_manual/getting_started/development_process.html#manual-backport

[kesselb]

Backport for stable25: #39591