Form import impossible due to formatDefaultValueForDB() return type error

Start at src/Glpi/Form/QuestionType/AbstractQuestionType.php line 56 and trace the call through src/Glpi/Form/Question.php and FormSerializer.php during form import. Reproduce the import with an advancedform LDAP field question, then verify that the default value is handled without the reported return-type error.

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GLPI Version

11.0.8

Plugin version

1.1.1

Bug description

Hi,

I'm facing this error when i try to import a form from my test environnement (identical) to prod environnement :
Uncaught PHP Exception TypeError: "Glpi\Form\QuestionType\AbstractQuestionType::formatDefaultValueForDB(): Return value must be of type ?string, array returned" at AbstractQuestionType.php line 56.

Test and prod environnements are the same.
My form has been created under previous GLPI 11.0.7 (without old plugin formcreator).

I've already import previous form without problem but this one use the advancedform list LDAP field questionType.

Thx

Relevant log output

[2026-07-07 07:57:12] glpi.CRITICAL:   *** Uncaught PHP Exception TypeError: "Glpi\Form\QuestionType\AbstractQuestionType::formatDefaultValueForDB(): Return value must be of type ?string, array returned" at AbstractQuestionType.php line 56
  Backtrace :
  ...i/Form/QuestionType/AbstractQuestionType.php:56 
  ./src/Glpi/Form/Question.php:395                   Glpi\Form\QuestionType\AbstractQuestionType->formatDefaultValueForDB()
  ./src/Glpi/Form/Question.php:278                   Glpi\Form\Question->prepareInput()
  ./src/CommonDBTM.php:1341                          Glpi\Form\Question->prepareInputForAdd()
  ...i/Form/Export/Serializer/FormSerializer.php:628 CommonDBTM->add()
  ...i/Form/Export/Serializer/FormSerializer.php:323 Glpi\Form\Export\Serializer\FormSerializer->importQuestions()
  ...i/Form/Export/Serializer/FormSerializer.php:307 Glpi\Form\Export\Serializer\FormSerializer->doImportFormFormSpecs()
  ...i/Form/Export/Serializer/FormSerializer.php:254 Glpi\Form\Export\Serializer\FormSerializer->importFormFromSpec()
  ...oller/Form/Import/Step4ExecuteController.php:75 Glpi\Form\Export\Serializer\FormSerializer->importFormsFromJson()
  ./vendor/symfony/http-kernel/HttpKernel.php:181    Glpi\Controller\Form\Import\Step4ExecuteController->__invoke()
  ./vendor/symfony/http-kernel/HttpKernel.php:76     Symfony\Component\HttpKernel\HttpKernel->handleRaw()
  ./vendor/symfony/http-kernel/Kernel.php:208        Symfony\Component\HttpKernel\HttpKernel->handle()
  ./public/index.php:71                              Symfony\Component\HttpKernel\Kernel->handle()

Page URL

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Steps To reproduce

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Your GLPI setup information

GLPI 11.0.8
PHP: 8.5.8 fpm-fcgi
Web server: Apache/2.4.67 (Debian) ()
Database: 10.11.14-MariaDB-0+deb12u2-log

Anything else?

No response