TYPO3 Core

When trying to delete an invalid Scheduler task (e.g. due to the related code being removed) an error occurs:

Fatal error: TYPO3\CMS\Scheduler\Scheduler::isValidTaskObject(): The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition &quot;<Task>&quot; of the object you are trying to operate on was loaded _before_ unserialize() gets called or provide a __autoload() function to load the class definition in /.../typo3/sysext/scheduler/Classes/Scheduler.php on line 449