Fix white screen when no license is present.

media_attribution.module

@@ -85,11 +85,13 @@ 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();
 
-  $referencedEntity = $variables['elements']['field_license']['#items']
-    ->first()->get('entity')->getTarget()->getValue();
-
-  $variables['license_link'] = $referencedEntity->get('field_license_link')->first()->view();
+    $variables['license_link'] = $referencedEntity->get('field_license_link')->first()->view();
+  }
 }
 
 /**
@@ -181,4 +183,4 @@ function media_attribution_theme() {
       'base hook' => 'field',
     ],
   ];
-}
+}