add validation on aggregators and filters

Export/Aggregator/NationalityAggregator.php

@@ -28,13 +28,16 @@ use Symfony\Component\Translation\TranslatorInterface;
 use Chill\MainBundle\Util\CountriesInfo;
 use Symfony\Component\Security\Core\Role\Role;
 use Chill\PersonBundle\Security\Authorization\PersonVoter;
+use Chill\MainBundle\Export\ExportElementValidatedInterface;
+use Symfony\Component\Validator\Context\ExecutionContextInterface;
 
 /**
  * 
  *
  * @author Julien Fastré <julien.fastre@champs-libres.coop>
  */
-class NationalityAggregator implements AggregatorInterface
+class NationalityAggregator implements AggregatorInterface,
+    ExportElementValidatedInterface
 {
     /**
      *
@@ -82,6 +85,14 @@ class NationalityAggregator implements AggregatorInterface
         ));
         
     }
+
+    public function validateForm($data, ExecutionContextInterface $context)
+    {
+        if ($data['group_by_level'] === null) {
+            $context->buildViolation("You should select an option")
+                ->addViolation();
+        }
+    }
     
     public function alterQuery(QueryBuilder $qb, $data)
     {