Are you sure the assignment to $res is correct as parent::manipulate($manipulation) (which targets SilverStripe\ORM\Connect\Database::manipulate()) seems to always return null.
This check looks for function or method calls that always return null and whose
return value is assigned to a variable.
silverstripe /
silverstripe-fulltextsearch
This check looks for function or method calls that always return null and whose return value is assigned to a variable.
The method
getObject()can return nothing but null, so it makes no sense to assign that value to a variable.The reason is most likely that a function or method is imcomplete or has been reduced for debug purposes.