ENGCOM-4427: [Backport] Issue Fixed: #8086: Multiline admin field is broken #21561

Author: sivaschenko

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

@@ -424,6 +424,11 @@ protected function _processGroup(
                 if (!isset($fieldData['value'])) {
                     $fieldData['value'] = null;
                 }
+                
+                if ($field->getType() == 'multiline' && is_array($fieldData['value'])) {
+                    $fieldData['value'] = trim(implode(PHP_EOL, $fieldData['value']));
+                }
+                
                 $data = [
                     'field' => $fieldId,
                     'groups' => $groups,