Issue #3114431 by jcandan, maurizio.ganovelli: Call to a member function addContent() on null

  if (!empty($group_ids)) {

    $plugin = 'group_node:' . $node->getType();

    foreach ($group_ids as $group_id) {

      // During node creation $group_id is an array, we need to extract target_id key.

      if (isset($group_id['target_id'])) {

        $group_id = $group_id['target_id'];

      }

      // Load the Group to be added to the node.

      $group = Drupal::entityTypeManager()->getStorage('group')->load($group_id);

      // Map node with chosen group.

      if ($group) {

        $group->addContent($node, $plugin);

      }

    }

  }

}