Document magic properties in extractor services

src/UriExtractor.php

@@ -41,6 +41,7 @@ class UriExtractor {
   public function extractUri(?object $input): ?string {
     $entity = $input;
     if ($input instanceof EntityReferenceFieldItemListInterface) {
+      /** @var \Drupal\Core\Field\Plugin\Field\FieldType\EntityReferenceItem $item */
       if ($item = $input->first()) {
         $entity = $item->entity;
       }

src/UrlExtractor.php

@@ -64,6 +64,7 @@ class UrlExtractor {
 
     $entity = $input;
     if ($input instanceof EntityReferenceFieldItemListInterface) {
+      /** @var \Drupal\Core\Field\Plugin\Field\FieldType\EntityReferenceItem $item */
       if ($item = $input->first()) {
         $entity = $item->entity;
       }