Issue #3238915: Refactor (if feasible) uses of the jQuery ready function to use VanillaJS

core/modules/migrate/src/Plugin/migrate/process/SubProcess.php

@@ -2,6 +2,7 @@
 
 namespace Drupal\migrate\Plugin\migrate\process;
 
+use Drupal\migrate\MigrateException;
 use Drupal\migrate\ProcessPluginBase;
 use Drupal\migrate\MigrateExecutableInterface;
 use Drupal\migrate\Row;
@@ -203,6 +204,9 @@ public function transform($value, MigrateExecutableInterface $migrate_executable
 
     if (is_array($value) || $value instanceof \Traversable) {
       foreach ($value as $key => $new_value) {
+        if (!is_array($new_value)) {
+          throw new MigrateException(sprintf("Input array should hold elements of type array, instead element was of type '%s'", gettype($new_value)));
+        }
         $new_row = new Row($new_value + $source);
         $migrate_executable->processRow($new_row, $this->configuration['process']);
         $destination = $new_row->getDestination();