Error message

• Deprecated function: htmlspecialchars(): Passing null to parameter #1 ($string) of type string is deprecated in Drupal\Component\Utility\Html::escape() (line 424 of core/lib/Drupal/Component/Utility/Html.php).

  Drupal\Component\Utility\Html::escape(NULL)
  array_map('Drupal\Component\Utility\Html::escape', Array) (Line: 58)
  simple_popup_blocks_page_attachments(Array) (Line: 313)
  Drupal\Core\Render\MainContent\HtmlRenderer->Drupal\Core\Render\MainContent\{closure}(Object, 'simple_popup_blocks') (Line: 405)
  Drupal\Core\Extension\ModuleHandler->invokeAllWith('page_attachments', Object) (Line: 314)
  Drupal\Core\Render\MainContent\HtmlRenderer->invokePageAttachmentHooks(Array) (Line: 288)
  Drupal\Core\Render\MainContent\HtmlRenderer->prepare(Array, Object, Object) (Line: 132)
  Drupal\Core\Render\MainContent\HtmlRenderer->renderResponse(Array, Object, Object) (Line: 90)
  Drupal\Core\EventSubscriber\MainContentViewSubscriber->onViewRenderArray(Object, 'kernel.view', Object)
  call_user_func(Array, Object, 'kernel.view', Object) (Line: 142)
  Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch(Object, 'kernel.view') (Line: 174)
  Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 81)
  Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 58)
  Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 48)
  Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 191)
  Drupal\page_cache\StackMiddleware\PageCache->fetch(Object, 1, 1) (Line: 128)
  Drupal\page_cache\StackMiddleware\PageCache->lookup(Object, 1, 1) (Line: 82)
  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: 23)
  Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 709)
  Drupal\Core\DrupalKernel->handle(Object) (Line: 19)
  

• Deprecated function: htmlspecialchars(): Passing null to parameter #1 ($string) of type string is deprecated in Drupal\Component\Utility\Html::escape() (line 424 of core/lib/Drupal/Component/Utility/Html.php).

  Drupal\Component\Utility\Html::escape(NULL)
  array_map('Drupal\Component\Utility\Html::escape', Array) (Line: 58)
  simple_popup_blocks_page_attachments(Array) (Line: 313)
  Drupal\Core\Render\MainContent\HtmlRenderer->Drupal\Core\Render\MainContent\{closure}(Object, 'simple_popup_blocks') (Line: 405)
  Drupal\Core\Extension\ModuleHandler->invokeAllWith('page_attachments', Object) (Line: 314)
  Drupal\Core\Render\MainContent\HtmlRenderer->invokePageAttachmentHooks(Array) (Line: 288)
  Drupal\Core\Render\MainContent\HtmlRenderer->prepare(Array, Object, Object) (Line: 132)
  Drupal\Core\Render\MainContent\HtmlRenderer->renderResponse(Array, Object, Object) (Line: 90)
  Drupal\Core\EventSubscriber\MainContentViewSubscriber->onViewRenderArray(Object, 'kernel.view', Object)
  call_user_func(Array, Object, 'kernel.view', Object) (Line: 142)
  Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch(Object, 'kernel.view') (Line: 174)
  Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 81)
  Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 58)
  Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 48)
  Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 191)
  Drupal\page_cache\StackMiddleware\PageCache->fetch(Object, 1, 1) (Line: 128)
  Drupal\page_cache\StackMiddleware\PageCache->lookup(Object, 1, 1) (Line: 82)
  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: 23)
  Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 709)
  Drupal\Core\DrupalKernel->handle(Object) (Line: 19)