Invalid argument supplied for foreach() in Checkboxes::valueCallback() on form

Problem/Motivation

When loading the page `admin/config/system/siteimprove` this error appears:

Warning: Invalid argument supplied for foreach() in Drupal\Core\Render\Element\Checkboxes::valueCallback() (line 100 of core/lib/Drupal/Core/Render/Element/Checkboxes.php).
Drupal\Core\Render\Element\Checkboxes::valueCallback(Array, , Object)
call_user_func_array(Array, Array) (Line: 1278)
Drupal\Core\Form\FormBuilder->handleInputElement('siteimprove_settings_form', Array, Object) (Line: 1001)
Drupal\Core\Form\FormBuilder->doBuildForm('siteimprove_settings_form', Array, Object) (Line: 1071)
Drupal\Core\Form\FormBuilder->doBuildForm('siteimprove_settings_form', Array, Object) (Line: 1071)
Drupal\Core\Form\FormBuilder->doBuildForm('siteimprove_settings_form', Array, Object) (Line: 1071)
Drupal\Core\Form\FormBuilder->doBuildForm('siteimprove_settings_form', Array, Object) (Line: 575)
Drupal\Core\Form\FormBuilder->processForm('siteimprove_settings_form', Array, Object) (Line: 321)
Drupal\Core\Form\FormBuilder->buildForm(Object, Object) (Line: 91)
Drupal\Core\Controller\FormController->getContentResult(Object, Object)
call_user_func_array(Array, Array) (Line: 123)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 573)
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: 151)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 68)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 57)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\KernelPreHandle->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: 47)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 52)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23)
Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 708)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)

Steps to reproduce

Load the admin form on `admin/config/system/siteimprove`.

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes