Fix fields extraction for form data

[MAILPOET-2754]

lib/Models/Form.php

@@ -59,7 +59,9 @@ class Form extends Model {
         && !empty($field['body'])
       ) {
         $nestedFields = $this->getFieldList($field['body']);
-        $fields = array_merge($fields, $nestedFields);
+        if ($nestedFields) {
+          $fields = array_merge($fields, $nestedFields);
+        }
         continue;
       }
 

tests/integration/Models/FormTest.php

@@ -117,6 +117,15 @@ class FormTest extends \MailPoetTest {
                 ],
               ],
             ],
+            [
+              'type' => 'column',
+              'body' => [
+                [
+                  'type' => 'divider',
+                  'id' => 'divider',
+                ],
+              ],
+            ],
           ],
         ],
         [