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

In the issueindex and node story migrations

web/modules/custom/geo_upgrade/migrations/upgrade_d7_node_issueindex.yml

@@ -165,9 +165,11 @@ process:
 #      process:
 #        target_id: tid
   field_publication_date:
+    - plugin: publication_date_default
+      source: field_publication_date
+      method: process
     -
       plugin: sub_process
-      source: created
       process:
         value:
           plugin: format_date

web/modules/custom/geo_upgrade/migrations/upgrade_d7_node_story.yml

@@ -213,8 +213,11 @@ process:
 #        target_id: tid
   field_publication_date:
     -
-      plugin: sub_process
+      plugin: publication_date_default
       source: field_publication_date
+      method: process
+    -
+      plugin: sub_process
       process:
         value:
           plugin: format_date

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;
+  }
+}