Fixed new Flex User erroring out on save (thanks @mikebi42)

CHANGELOG.md

@@ -5,6 +5,7 @@
     * Changed `Folder::hasChildren` to `Folder::countChildren`
 1. [](#bugfix)
     * Fixed new `Flex Page` not having correct form fields for the page type
+    * Fixed new `Flex User` erroring out on save (thanks @mikebi42)
     * Fixed blueprint value filtering in lists [#2923](https://github.com/getgrav/grav/issues/2923)
 
 # v1.7.0-rc.11

system/src/Grav/Common/Flex/Types/Users/UserIndex.php

@@ -57,7 +57,7 @@ class UserIndex extends FlexIndex
     public static function updateObjectMeta(array &$meta, array $data)
     {
         // Username can also be number and stored as such.
-        $key = (string)($data['username'] ?? $meta['key']);
+        $key = (string)($data['username'] ?? $meta['key'] ?? $meta['storage_key']);
         $meta['key'] = mb_strtolower($key);
         $meta['email'] = isset($data['email']) ? mb_strtolower($data['email']) : null;
     }