covers edge case for Luhn

src/Symfony/Component/Validator/Constraints/LuhnValidator.php

@@ -51,7 +51,7 @@ class LuhnValidator extends ConstraintValidator
             $sum += (($i % 2) === $oddLength) ? array_sum(str_split($digit * 2)) : $digit;
         }
 
-        if (($sum % 10) !== 0) {
+        if ($sum === 0 || ($sum % 10) !== 0) {
             $this->context->addViolation($constraint->message);
         }
     }

src/Symfony/Component/Validator/Tests/Constraints/LuhnValidatorTest.php

@@ -102,6 +102,8 @@ class LuhnValidatorTest extends \PHPUnit_Framework_TestCase
         return array(
             array('1234567812345678'),
             array('4222222222222222'),
+            array('0000000000000000'),
+            array(0),
         );
     }
 }