.../Normalizer/EntityReferenceItemNormalizer.php    | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/core/modules/hal/src/Normalizer/EntityReferenceItemNormalizer.php b/core/modules/hal/src/Normalizer/EntityReferenceItemNormalizer.php
index 263612d..d103894 100644
--- a/core/modules/hal/src/Normalizer/EntityReferenceItemNormalizer.php
+++ b/core/modules/hal/src/Normalizer/EntityReferenceItemNormalizer.php
@@ -49,10 +49,10 @@ class EntityReferenceItemNormalizer extends FieldItemNormalizer implements UuidR
    *   The hypermedia link manager.
    * @param \Drupal\serialization\EntityResolver\EntityResolverInterface $entity_Resolver
    *   The entity resolver.
-   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface|null $entity_type_manager
    *   The entity type manager.
    */
-  public function __construct(LinkManagerInterface $link_manager, EntityResolverInterface $entity_Resolver, EntityTypeManagerInterface $entity_type_manager) {
+  public function __construct(LinkManagerInterface $link_manager, EntityResolverInterface $entity_Resolver, EntityTypeManagerInterface $entity_type_manager = NULL) {
     $this->linkManager = $link_manager;
     $this->entityResolver = $entity_Resolver;
     $this->entityTypeManager = $entity_type_manager;
@@ -130,7 +130,7 @@ protected function targetEntityIsFieldable(EntityReferenceItem $item) {
     }
 
     // Otherwise, we need to get the class for the type.
-    $target_entity_type = $this->entityTypeManager->getDefinition($target_entity_type_id);
+    $target_entity_type = $this->getEntityTypeManager()->getDefinition($target_entity_type_id);
     $target_entity_type_class = $target_entity_type->getClass();
 
     return is_a($target_entity_type_class, FieldableEntityInterface::class, TRUE);
@@ -164,4 +164,19 @@ public function getUuid($data) {
     }
   }
 
+  /**
+   * Gets the entity type manager.
+   *
+   * @return \Drupal\Core\Entity\EntityTypeManagerInterface|mixed
+   *
+   * @internal
+   * @todo Remove in Drupal 9.0.0. Only exists to provide constructor BC.
+   */
+  protected function getEntityTypeManager() {
+    if (!isset($this->entityTypeManager)) {
+      $this->entityTypeManager = \Drupal::service('entity_type.manager');
+    }
+    return $this->entityTypeManager;
+  }
+
 }