typo

src/Symfony/Bridge/Doctrine/Validator/Constraints/UniqueEntityValidator.php

@@ -50,7 +50,7 @@ class UniqueEntityValidator extends ConstraintValidator
 
         $fields = (array)$constraint->fields;
 
-        if (count($constraint->fields) == 0) {
+        if (count($fields) == 0) {
             throw new ConstraintDefinitionException("At least one field has to be specified.");
         }