diff -u b/core/lib/Drupal/Core/Entity/EntityInterface.php b/core/lib/Drupal/Core/Entity/EntityInterface.php
--- b/core/lib/Drupal/Core/Entity/EntityInterface.php
+++ b/core/lib/Drupal/Core/Entity/EntityInterface.php
@@ -20,7 +20,7 @@
    * The UUID is guaranteed to be unique and can be used to identify an entity
    * across multiple systems.
    *
-   * @return string
+   * @return string|null
    *   The UUID of the entity, or NULL if the entity does not have one.
    */
   public function uuid();
@@ -89,7 +89,7 @@
   /**
    * Returns the label of the entity.
    *
-   * @return string
+   * @return string|null
    *   The label of the entity, or NULL if there is no label defined.
    */
   public function label();