Error message
Deprecated function: mb_strtolower(): Passing null to parameter #1 ($string) of type string is deprecated in Drupal\views\Plugin\views\HandlerBase->caseTransform() (line 251 of core/modules/views/src/Plugin/views/HandlerBase.php).
Drupal\views\Plugin\views\HandlerBase->caseTransform() (Line: 275)
Drupal\views\Plugin\views\argument\StringArgument->summaryArgument() (Line: 366)
template_preprocess_views_view_summary_unformatted()
call_user_func_array() (Line: 261)
Drupal\Core\Theme\ThemeManager->render() (Line: 491)
Drupal\Core\Render\Renderer->doRender() (Line: 248)
Drupal\Core\Render\Renderer->render() (Line: 484)
Drupal\Core\Template\TwigExtension->escapeFilter() (Line: 113)
__TwigTemplate_cfe256946ef123df7fca91bec1254fc3->doDisplay() (Line: 387)
Twig\Template->yield() (Line: 343)
Twig\Template->display() (Line: 358)
Twig\Template->render() (Line: 35)
Twig\TemplateWrapper->render() (Line: 33)
twig_render_template() (Line: 348)
Drupal\Core\Theme\ThemeManager->render() (Line: 491)
Drupal\Core\Render\Renderer->doRender() (Line: 504)
Drupal\Core\Render\Renderer->doRender() (Line: 504)
Drupal\Core\Render\Renderer->doRender() (Line: 248)
Drupal\Core\Render\Renderer->render() (Line: 484)
Drupal\Core\Template\TwigExtension->escapeFilter() (Line: 101)
__TwigTemplate_cfe256946ef123df7fca91bec1254fc3->doDisplay() (Line: 387)
Twig\Template->yield() (Line: 343)
Twig\Template->display() (Line: 358)
Twig\Template->render() (Line: 35)
Twig\TemplateWrapper->render() (Line: 33)
twig_render_template() (Line: 348)
Drupal\Core\Theme\ThemeManager->render() (Line: 491)
Drupal\Core\Render\Renderer->doRender() (Line: 504)
Drupal\Core\Render\Renderer->doRender() (Line: 248)
Drupal\Core\Render\Renderer->render() (Line: 238)
Drupal\Core\Render\MainContent\HtmlRenderer->Drupal\Core\Render\MainContent\{closure}() (Line: 638)
Drupal\Core\Render\Renderer->executeInRenderContext() (Line: 239)
Drupal\Core\Render\MainContent\HtmlRenderer->prepare() (Line: 128)
Drupal\Core\Render\MainContent\HtmlRenderer->renderResponse() (Line: 90)
Drupal\Core\EventSubscriber\MainContentViewSubscriber->onViewRenderArray()
call_user_func() (Line: 111)
Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch() (Line: 186)
Symfony\Component\HttpKernel\HttpKernel->handleRaw() (Line: 76)
Symfony\Component\HttpKernel\HttpKernel->handle() (Line: 53)
Drupal\Core\StackMiddleware\Session->handle() (Line: 48)
Drupal\Core\StackMiddleware\KernelPreHandle->handle() (Line: 28)
Drupal\Core\StackMiddleware\ContentLength->handle() (Line: 201)
Drupal\page_cache\StackMiddleware\PageCache->fetch() (Line: 138)
Drupal\page_cache\StackMiddleware\PageCache->lookup() (Line: 87)
Drupal\page_cache\StackMiddleware\PageCache->handle() (Line: 48)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle() (Line: 51)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle() (Line: 36)
Drupal\Core\StackMiddleware\AjaxPageState->handle() (Line: 51)
Drupal\Core\StackMiddleware\StackedHttpKernel->handle() (Line: 741)
Drupal\Core\DrupalKernel->handle() (Line: 19)
