Fatal error after import on multilingual sites

Problem/Motivation

The website encountered an unexpected error. Try again later.

TypeError: array_key_exists(): Argument #2 ($array) must be of type array, Drupal\Core\StringTranslation\TranslatableMarkup given in array_key_exists() (line 140 of modules/contrib/licenses_vocabulary/src/Form/LicensesImportForm.php).

Drupal\licenses_vocabulary\Form\LicensesImportForm->validateForm(Array, Object)
call_user_func_array(Array, Array) (Line: 82)
Drupal\Core\Form\FormValidator->executeValidateHandlers(Array, Object) (Line: 274)
Drupal\Core\Form\FormValidator->doValidateForm(Array, Object, 'licenses_import_form') (Line: 118)
Drupal\Core\Form\FormValidator->validateForm('licenses_import_form', Array, Object) (Line: 593)
Drupal\Core\Form\FormBuilder->processForm('licenses_import_form', Array, Object) (Line: 326)
Drupal\Core\Form\FormBuilder->buildForm(Object, Object) (Line: 73)
Drupal\Core\Controller\FormController->getContentResult(Object, Object)
call_user_func_array(Array, Array) (Line: 123)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 638)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 124)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array) (Line: 97)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 181)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 76)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 68)
Drupal\simple_oauth\HttpMiddleware\BasicAuthSwap->handle(Object, 1, 1) (Line: 53)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 48)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 28)
Drupal\Core\StackMiddleware\ContentLength->handle(Object, 1, 1) (Line: 32)
Drupal\big_pipe\StackMiddleware\ContentLength->handle(Object, 1, 1) (Line: 106)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1) (Line: 85)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 48)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 51)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 36)
Drupal\Core\StackMiddleware\AjaxPageState->handle(Object, 1, 1) (Line: 51)
Drupal\Core\StackMiddleware\StackedHttpKernel->handle(Object, 1, 1) (Line: 741)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)

Steps to reproduce

Install module.

Note that the icons and URLs have not been saved for each license term. (At least when installed as part of a site install with existing configuration.)

Delete each term.

Paste in the contents of licenses_vocabulary.default.licenses.yml (minus the leading ---) into the form at /admin/config/content/licenses_import

Press (the questionably-named) "Save configuration" button.

(Despite the fatal error, the terms are created successfully, though if their files had been deleted it would have given a form error.)

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes