Notice: Only variables should be passed by reference

Hi,

I have problem with using this module on my installation.
Here is error message:

Notice: Only variables should be passed by reference in Drupal\webform_node_element\Element\WebformNodeElement::preRenderWebformNodeElement() (line 48 of modules/contrib/webform_node_element/src/Element/WebformNodeElement.php).
Drupal\webform_node_element\Element\WebformNodeElement::preRenderWebformNodeElement(Array)
call_user_func(Array, Array) (Line: 378)
Drupal\Core\Render\Renderer->doRender(Array) (Line: 450)
Drupal\Core\Render\Renderer->doRender(Array) (Line: 450)
Drupal\Core\Render\Renderer->doRender(Array) (Line: 450)
Drupal\Core\Render\Renderer->doRender(Array, ) (Line: 195)
Drupal\Core\Render\Renderer->render(Array, ) (Line: 226)
Drupal\Core\Render\MainContent\HtmlRenderer->Drupal\Core\Render\MainContent\{closure}() (Line: 576)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 227)
Drupal\Core\Render\MainContent\HtmlRenderer->prepare(Array, Object, Object) (Line: 117)
Drupal\Core\Render\MainContent\HtmlRenderer->renderResponse(Array, Object, Object) (Line: 90)
Drupal\Core\EventSubscriber\MainContentViewSubscriber->onViewRenderArray(Object, 'kernel.view', Object) (Line: 108)
Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch('kernel.view', Object) (Line: 158)
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: 99)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1) (Line: 78)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 50)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23)
Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 657)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)

Here is drush status:

landsman2-mbp:docroot michal.landsman$ drush status
 Drupal version                  :  8.4.3                                                     
 Site URI                        :  wedding                                                   
 Database driver                 :  mysql                                                     
 Database hostname               :  127.0.0.1                                                 
 Database port                   :  3306                                                      
 Database username               :  root                                                      
 Database name                   :  marianne-wedding                                          
 Database                        :  Connected                                                 
 Drupal bootstrap                :  Successful                                                
 Drupal user                     :                                                            
 Default theme                   :  thunder_base                                              
 Administration theme            :  thunder_admin                                             
 PHP configuration               :  /Applications/MAMP/bin/php/php7.1.8/conf/php.ini          
 PHP OS                          :  Darwin                                                    
 Drush script                    :  /usr/local/bin/drush                                      
 Drush version                   :  8.1.15                                                    
 Drush temp directory            :  /tmp                                                      
 Drush configuration             :                                                            
 Drush alias files               :                                                            
 Install profile                 :  thunder                                                   
 Drupal root                     :  /Users/michal.landsman/localhost/marianne-thunder/docroot 
 Drupal Settings File            :  sites/wedding/settings.php                                
 Site path                       :  sites/wedding                                             
 File directory path             :  sites/default/files/public                                
 Private file directory path     :  sites/default/files/private                               
 Temporary file directory path   :  /Applications/MAMP/tmp/php                                
 Sync config path                :  ../config/wedding/sync    

I am using webform on multi-site installation