Fixing problem when id is not set in find. This also resolve problem …

…with master-detail forms when master has not been persisted. -sonata-project/SonataAdminBundle#259

Model/ModelManager.php

@@ -138,6 +138,10 @@ public function delete($object)
      */
     public function find($class, $id)
     {
+        if ( !isset($id) ) {
+            return null;
+        }
+
         $values = array_combine($this->getIdentifierFieldNames($class), explode(self::ID_SEPARATOR, $id));
         return $this->getEntityManager($class)->getRepository($class)->find($values);
     }