From 315cc30a1a7dcb6b40ab6a9ee2592aa4611332a8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jan=20B=C3=B6hmer?= <jan.h.boehmer@gmx.de>
Date: Mon, 6 Apr 2020 11:52:42 +0200
Subject: [PATCH] Fix error with reindexed collectionType when multiple parts
 dont have IDs yet.

---
 src/Form/CollectionTypeExtension.php | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/Form/CollectionTypeExtension.php b/src/Form/CollectionTypeExtension.php
index 53a06b56..01bc6a89 100644
--- a/src/Form/CollectionTypeExtension.php
+++ b/src/Form/CollectionTypeExtension.php
@@ -84,7 +84,9 @@ class CollectionTypeExtension extends AbstractTypeExtension
                 $error_mapping = [];
 
                 foreach ($data->toArray() as $key => $item) {
-                    $index = $options['reindex_prefix'] . $this->propertyAccess->getValue($item, $options['reindex_path']);
+                    $id = $this->propertyAccess->getValue($item, $options['reindex_path']);
+                    //If element has an ID then use it. otherwise use default key
+                    $index = $id === null ? $key : $options['reindex_prefix'] . $id;
                     $error_mapping['[' . $key . ']'] = $index;
                     $reindexed_data->set($index, $item);
                 }