[Bug]: Data Importer stuck on import loading

[benshen-secretlab]

Studio API version

2026.1.4

Steps to reproduce

Root caused: explode only accept string, but default value given array

Log

[2026-05-29T11:15:37.547466+08:00] messenger.CRITICAL: Error thrown while handling message Pimcore\Bundle\DataImporterBundle\Messenger\DataImporterMessage. Removing from transport after 3 retries. Error: "Handling "Pimcore\Bundle\DataImporterBundle\Messenger\DataImporterMessage" failed: explode(): Argument #2 ($string) must be of type string, array given" {"class":"Pimcore\\Bundle\\DataImporterBundle\\Messenger\\DataImporterMessage","message_id":null,"retryCount":3,"error":"Handling \"Pimcore\\Bundle\\DataImporterBundle\\Messenger\\DataImporterMessage\" failed: explode(): Argument #2 ($string) must be of type string, array given","exception":"[object] (Symfony\\Component\\Messenger\\Exception\\HandlerFailedException(code: 0): Handling \"Pimcore\\Bundle\\DataImporterBundle\\Messenger\\DataImporterMessage\" failed: explode(): Argument #2 ($string) must be of type string, array given at /var/www/html/pimcore_demo/vendor/symfony/messenger/Middleware/HandleMessageMiddleware.php:121)\n[previous exception] [object] (TypeError(code: 0): explode(): Argument #2 ($string) must be of type string, array given at /var/www/html/pimcore_demo/vendor/pimcore/data-importer/src/Mapping/DataTarget/Classificationstore.php:37)"} []
[2026-05-29T11:15:37.579077+08:00] messenger.CRITICAL: Error thrown while handling message Pimcore\Bundle\DataImporterBundle\Messenger\DataImporterMessage. Removing from transport after 3 retries. Error: "Handling "Pimcore\Bundle\DataImporterBundle\Messenger\DataImporterMessage" failed: explode(): Argument #2 ($string) must be of type string, array given" {"class":"Pimcore\\Bundle\\DataImporterBundle\\Messenger\\DataImporterMessage","message_id":null,"retryCount":3,"error":"Handling \"Pimcore\\Bundle\\DataImporterBundle\\Messenger\\DataImporterMessage\" failed: explode(): Argument #2 ($string) must be of type string, array given","exception":"[object] (Symfony\\Component\\Messenger\\Exception\\HandlerFailedException(code: 0): Handling \"Pimcore\\Bundle\\DataImporterBundle\\Messenger\\DataImporterMessage\" failed: explode(): Argument #2 ($string) must be of type string, array given at /var/www/html/pimcore_demo/vendor/symfony/messenger/Middleware/HandleMessageMiddleware.php:121)\n[previous exception] [object] (TypeError(code: 0): explode(): Argument #2 ($string) must be of type string, array given at /var/www/html/pimcore_demo/vendor/pimcore/data-importer/src/Mapping/DataTarget/Classificationstore.php:37)"} []

Actual Behavior

Import stuck loading forever.

Expected Behavior

Import should able to execute without stuck