diff --git a/src/EventSubscriber/WorkbenchTransitionEventSubscriber.php b/src/EventSubscriber/WorkbenchTransitionEventSubscriber.php
index 6aec1f0..db7e022 100644
--- a/src/EventSubscriber/WorkbenchTransitionEventSubscriber.php
+++ b/src/EventSubscriber/WorkbenchTransitionEventSubscriber.php
@@ -147,7 +147,7 @@ class WorkbenchTransitionEventSubscriber implements EventSubscriberInterface {
         $recipients[] = $field_item->get('value')->getValue();
       }
     }
-    return array_unique($recipients);
+    return array_filter(array_unique($recipients));
   }
 
 
diff --git a/tests/src/Functional/WorkbenchTransitionEmailTest.php b/tests/src/Functional/WorkbenchTransitionEmailTest.php
index 0b9191c..48cc739 100644
--- a/tests/src/Functional/WorkbenchTransitionEmailTest.php
+++ b/tests/src/Functional/WorkbenchTransitionEmailTest.php
@@ -74,6 +74,13 @@ class WorkbenchTransitionEmailTest extends BrowserTestBase {
   protected $approver3;
 
   /**
+   * Approver 4 - no email address.
+   *
+   * @var \Drupal\user\UserInterface
+   */
+  protected $approver4;
+
+  /**
    * Editor.
    *
    * @var \Drupal\user\UserInterface
@@ -145,6 +152,11 @@ class WorkbenchTransitionEmailTest extends BrowserTestBase {
     $this->approver3->addRole('approver');
     $this->approver3->block();
     $this->approver3->save();
+    $this->approver4 = $this->drupalCreateUser();
+    $this->approver4->addRole('approver');
+    $this->approver4->setEmail(NULL);
+    $this->approver4->save();
+
     // Create a editor role and user.
     $this->editorRole = $this->drupalCreateRole([
       'view any unpublished content',