Fix filter path null error

Author: loostro

Form/EventListener/CollectionUploadSubscriber.php

@@ -218,8 +218,20 @@ public function postSubmit(FormEvent $event)
         $form = $event->getForm();
         $data = $form->getParent()->getData();
 
+        $current = $form;
+        $isAllValid = true;
+
+        // check recuresively this form and all it's parents
+        do {
+            if (!$current->isValid()) {
+                $isAllValid = false;
+                break;
+            }
+            $current = $current->getParent();
+        } while (null !== $current);
+
         $getter = 'get'.ucfirst($this->propertyName);
-        if (!$form->isValid() && $data->$getter() instanceof ArrayCollection) {
+        if (!$isAllValid && $data->$getter() instanceof ArrayCollection) {
             // remove files absent in the original collection
             $data->$getter()->clear();