Errors when we edit a node if no configuration has done

There are errors when module Save & Edit is just enabled and Settings form is not submitted :
$config->get('node_types') returns NULL

    Warning: array_values() expects parameter 1 to be array, null given in save_edit_form_alter() (line 42 of modules/contrib_project/save_edit/save_edit.module).

    save_edit_form_alter(Array, Object, 'node_page_edit_form') (Line: 539)
    Drupal\Core\Extension\ModuleHandler->alter('form', Array, Object, 'node_page_edit_form') (Line: 835)
    Drupal\Core\Form\FormBuilder->prepareForm('node_page_edit_form', Array, Object) (Line: 277)
    Drupal\Core\Form\FormBuilder->buildForm(Object, Object) (Line: 93)
    Drupal\Core\Controller\FormController->getContentResult(Object, Object)
    call_user_func_array(Array, Array) (Line: 123)
    Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 582)
    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: 693)
    Drupal\Core\DrupalKernel->handle(Object) (Line: 19)

    Warning: in_array() expects parameter 2 to be array, null given in save_edit_form_alter() (line 42 of modules/contrib_project/save_edit/save_edit.module).

    save_edit_form_alter(Array, Object, 'node_page_edit_form') (Line: 539)
    Drupal\Core\Extension\ModuleHandler->alter('form', Array, Object, 'node_page_edit_form') (Line: 835)
    Drupal\Core\Form\FormBuilder->prepareForm('node_page_edit_form', Array, Object) (Line: 277)
    Drupal\Core\Form\FormBuilder->buildForm(Object, Object) (Line: 93)
    Drupal\Core\Controller\FormController->getContentResult(Object, Object)
    call_user_func_array(Array, Array) (Line: 123)
    Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 582)
    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: 693)
    Drupal\Core\DrupalKernel->handle(Object) (Line: 19)