adapt elements to new interface definition

Export/Aggregator/NationalityAggregator.php

@@ -125,9 +125,9 @@ class NationalityAggregator implements AggregatorInterface
         return array('nationality_aggregator');
     }
     
-    public function requiredRole()
+    public function addRole()
     {
-        return new Role(PersonVoter::STATS);
+        return NULL;
     }
     
     public function getLabels($key, array $values, $data)