[PHP 8.x] Deprecated functionality: strtotime(): Passing null to parameter #1 ($datetime)

[addison74]

[Test Environment]

Windows 11 + WSL
Docker 4.34.4
DDEV 1.2.5 (Apache 2.4.62, PHP 8.4.ORC1, MariaDB 10.11.9) with MAGE_IS_DEVELOPER_MODE=1
Magento Sample Data

Steps to reproduce this issue

Go to Backend > Catalog > Manage Products
Edit any product from the grid
Add Related/Cross/Up sells to the product then Save

The product changes are saved but you will see this error message

Deprecated functionality: strtotime(): Passing null to parameter #1 ($datetime)
of type string is deprecated in 
/var/www/html/app/code/core/Mage/CatalogRule/Model/Resource/Rule.php on line 187

[sreichel]

@all-contributors add @addison74 bug

[allcontributors]

@sreichel

I've put up a pull request to add @addison74! 🎉