diff -u b/core/lib/Drupal/Core/Session/AccountInterface.php b/core/lib/Drupal/Core/Session/AccountInterface.php
--- b/core/lib/Drupal/Core/Session/AccountInterface.php
+++ b/core/lib/Drupal/Core/Session/AccountInterface.php
@@ -148,7 +148,7 @@
   /**
    * Returns the email address of this account if it exists.
    *
-   * @return string|NULL
+   * @return string|null
    *   The email address, or NULL if the account is anonymous or the user does
    *   not have an email address.
    */