Update to Drupal 8.1.0. For more information, see https://www.drupal.org/drupal-8.1.0-release-notes

vendor/symfony/validator/Constraints/Blank.php

@@ -21,5 +21,11 @@ use Symfony\Component\Validator\Constraint;
  */
 class Blank extends Constraint
 {
+    const NOT_BLANK_ERROR = '183ad2de-533d-4796-a439-6d3c3852b549';
+
+    protected static $errorNames = array(
+        self::NOT_BLANK_ERROR => 'NOT_BLANK_ERROR',
+    );
+
     public $message = 'This value should be blank.';
 }