MAGETWO-93192: Config backend models are not populated with fieldset data

Author: dhorytskyi

app/code/Magento/Config/Model/Config.php

@@ -360,6 +360,10 @@ protected function _processGroup(
             // set value for group field entry by fieldname
             // use extra memory
             $fieldsetData = [];
+            foreach ($groupData['fields'] as $fieldId => $fieldData) {
+                $fieldsetData[$fieldId] = $fieldData['value'] ?? null;
+            }
+
             foreach ($groupData['fields'] as $fieldId => $fieldData) {
                 $isReadOnly = $this->settingChecker->isReadOnly(
                     $groupPath . '/' . $fieldId,
@@ -380,7 +384,6 @@ protected function _processGroup(
                 if (!isset($fieldData['value'])) {
                     $fieldData['value'] = null;
                 }
-                $fieldsetData[$fieldId] = $fieldData['value'];
                 $data = [
                     'field' => $fieldId,
                     'groups' => $groups,