Fix white screen when no license is present.

media_attribution.module

@@ -85,12 +85,14 @@ function media_attribution_preprocess_field__paragraph__field_attribution_author
 
 function media_attribution_preprocess_paragraph__license_attribution__license_attribution(&$variables) {
   $variables['license_prefix'] = \Drupal::translation()->translate('Licensed under');
-
+  $items = $variables['elements']['field_license']['#items'];
+  if (!empty($items)) {
     $referencedEntity = $variables['elements']['field_license']['#items']
       ->first()->get('entity')->getTarget()->getValue();
 
     $variables['license_link'] = $referencedEntity->get('field_license_link')->first()->view();
   }
+}
 
 /**
  * Implementation of hook_preprocess_entity_embed_container().