Add the "publication date" default value in the blog and gleaning types

web/modules/custom/geo_upgrade/src/Plugin/migrate/process/PublicationDateDefault.php

@@ -20,7 +20,7 @@ class PublicationDateDefault extends ProcessPluginBase {
    */
   public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
     $created_date = $row->getSourceProperty('created');
-    if (empty($value)) {
+    if (!isset($value) || empty($value)) {
       $value = [0 => ['value' => date('Y-m-d\TH:i:s', $created_date)]];
     }
     return $value;