Fix property_exists(): Passing null to parameter #2 ($property) of type string is deprecated

[jdreesen]

Fixes:

Deprecated: property_exists(): Passing null to parameter #2 ($property) of type string is deprecated in /var/www/pimcore/vendor/pimcore/pimcore/models/DataObject/Traits/ObjectVarTrait.php on line 53

[github-actions]

Review Checklist

• Target branch (10.5 for bug fixes, others 11.x)
• Tests (if it's testable code, there should be a test for it - get help)
• Docs (every functionality needs to be documented, see here)
• Migration incl. install.sql (e.g. if the database schema changes, ...)
• Upgrade notes (deprecations, important information, migration hints, ...)
• Label
• Milestone

[blankse]

Should we also change the php doc to @param string|null $var if $var can be null?

[mcop1]

As always, thank you guys 👍