Issue #2819901 by mikeryan: Add 'class' to migration configuration entity schema

config/schema/migrate_plus.schema.yml

@@ -7,6 +7,9 @@ migrate_plus.migration.*:
     id:
       type: string
       label: 'ID'
+    class:
+      type: string
+      label: 'Class'
     migration_tags:
       type: sequence
       label: 'Migration Tags'

migrate_plus.module

@@ -18,6 +18,11 @@ use Drupal\migrate_plus\Event\MigratePrepareRowEvent;
 function migrate_plus_migration_plugins_alter(array &$migrations) {
   /** @var \Drupal\migrate\Plugin\MigrationInterface $migration */
   foreach ($migrations as $id => $migration) {
+    // Add the default class where empty.
+    if (empty($migration['class'])) {
+      $migrations[$id]['class'] = 'Drupal\migrate\Plugin\Migration';
+    }
+
     if (empty($migration['migration_group'])) {
       $migration['migration_group'] = 'default';
     }