Marcin Grabias
--- a/src/Hook/CourseMembershipHooksBase.php
+++ b/src/Hook/CourseMembershipHooksBase.php
      '#description' => $self_join ? $this->t('You will be added to the selected class.') : $this->t('Student will be added to the selected class.'),
      '#options' => $options,
    ];
+
+    if (\array_key_exists('group_roles', $form)) {
+      $form['group_roles']['#states'] = [
+        'visible' => [
+          'select[name=class]' => ['value' => '0'],