The default value of "field_publication_date" is now the created date

In the issueindex and node story migrations

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

@@ -0,0 +1,28 @@
+<?php
+
+
+namespace Drupal\geo_upgrade\Plugin\migrate\process;
+
+use Drupal\migrate\MigrateExecutableInterface;
+use Drupal\migrate\MigrateSkipRowException;
+use Drupal\migrate\ProcessPluginBase;
+use Drupal\migrate\Row;
+
+/**
+ * @MigrateProcessPlugin(
+ *   id = "publication_date_default",
+ *   handle_multiples = TRUE
+ * )
+ */
+class PublicationDateDefault extends ProcessPluginBase {
+  /**
+   * {@inheritdoc}
+   */
+  public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
+    $created_date = $row->getSourceProperty('created');
+    if (empty($value)) {
+      $value = [0 => ['value' => date('Y-m-d\TH:i:s', $created_date)]];
+    }
+    return $value;
+  }
+}