diff -u b/core/tests/Drupal/Tests/Core/Entity/EntityManagerTest.php b/core/tests/Drupal/Tests/Core/Entity/EntityManagerTest.php
--- b/core/tests/Drupal/Tests/Core/Entity/EntityManagerTest.php
+++ b/core/tests/Drupal/Tests/Core/Entity/EntityManagerTest.php
@@ -1401,6 +1401,37 @@
     return get_class($this->getMockForAbstractClass('Drupal\Core\Entity\EntityHandlerBase'));
   }
 
+  /**
+   * Tests the loadEntityByUuid() method.
+   *
+   * @covers ::loadEntityByUuid
+   *
+   * @dataProvider providerTestLoadEntityByUuid
+   */
+  public function testloadEntityByUuid($entity_type_id, $uuid) {
+    $entity = $this->getMock('Drupal\Core\Entity\EntityTypeInterface');
+    $this->setUpEntityManager(array(
+        'apple' => $entity,
+        'banana' => $entity,
+    ));
+
+    $new_entity = $this->entityManager->loadEntityByUuid($entity_type_id,$uuid);
+    $this->assertNull($new_entity);
+  }
+
+  /**
+   * Provides test data for testloadEntityByUuid().
+   *
+   * @return array
+   *   Test data.
+   */
+  public function providerTestLoadEntityByUuid() {
+    return array(
+      array('apple', 2415),
+      array('banana', NULL),
+    );
+  }
+
 }
 
 /*
@@ -1545,37 +1576,6 @@
     return get_class($this->getMockForAbstractClass('Drupal\Core\Entity\EntityHandlerBase'));
   }
 
-  /**
-   * Tests the loadEntityByUuid() method.
-   *
-   * @covers ::loadEntityByUuid()
-   * 
-   * @dataProvider providerTestLoadEntityByUuid
-   */
-  public function testloadEntityByUuid($entity_type_id, $uuid) {
-    $entity = $this->getMock('Drupal\Core\Entity\EntityManager');
-    $this->setUpEntityManager(array(
-      'apple' => $entity,
-      'banana' => $entity,
-    ));
-
-    $new_entity = $this->entityManager->loadEntityByUuid($entity_type_id,$uuid);
-    $this->assertNull($new_entity);
-  }
-  
-  /**
-   * Provides test data for testloadEntityByUuid().
-   *
-   * @return array
-   *   Test data.
-   */
-  public function providerTestLoadEntityByUuid() {
-    return array(
-      array('apple', 2415),
-      array('banana', NULL),
-    );
-  }
-
 }
 
 /*
only in patch2:
unchanged:
--- a/core/lib/Drupal/Core/Entity/EntityManager.php
+++ b/core/lib/Drupal/Core/Entity/EntityManager.php
@@ -9,6 +9,7 @@
 
 use Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException;
 use Drupal\Component\Plugin\Exception\PluginNotFoundException;
+use Drupal\Component\Uuid\Uuid;
 use Drupal\Component\Utility\String;
 use Drupal\Core\Cache\Cache;
 use Drupal\Core\Cache\CacheBackendInterface;
@@ -968,6 +969,10 @@ protected function getDisplayModeOptions($display_type, $entity_type_id, $includ
    * {@inheritdoc}
    */
   public function loadEntityByUuid($entity_type_id, $uuid) {
+    // Return NULL for invalid UUID's.
+    if (empty($uuid) || !Uuid::isValid($uuid)) {
+      return NULL;
+    }
     $entity_type = $this->getDefinition($entity_type_id);
 
     if (!$uuid_key = $entity_type->getKey('uuid')) {
@@ -976,6 +981,10 @@ public function loadEntityByUuid($entity_type_id, $uuid) {
 
     $entities = $this->getStorage($entity_type_id)->loadByProperties(array($uuid_key => $uuid));
 
+    if (empty($entities)) {
+      return NULL;
+    }
+
     return reset($entities);
   }