reverted:
--- b/core/modules/config/lib/Drupal/config/Tests/ConfigEntityTest.php
+++ a/core/modules/config/lib/Drupal/config/Tests/ConfigEntityTest.php
@@ -146,7 +146,7 @@
     // Verify that the entity was overwritten.
     $same_id = entity_load('config_test', $config_test->id());
     $this->assertIdentical($same_id->id(), $config_test->id());
+    $this->assertIdentical($same_id->label(), NULL);
-    $this->assertIdentical($same_id->label(), '');
     $this->assertNotEqual($same_id->uuid(), $config_test->uuid());
 
     // Delete the overridden entity first.