蒙戈例外 没有提供任何文件

我在我的symfony项目中使用MongoDB。为了与数据库进行通信，我正在使用文档管理器和MongoClient。

我打算做的是将数组直接批量插入数据库。我已经尝试创建数组并填充它。但是当我执行批处理插入((时，我得到这个异常

[MongoException]    
 no documents given

非常令人困惑，因为根据手册，如果插入的数组为空，则会引发异常。我已经确保并尝试了很多次，我插入的数组不是空的。这是我的代码：

$dm = $this->getContainer()->get('doctrine_mongodb');
            echo "initiating... 'n";
        $data = $dm->getRepository("KahviDocumentBundle:Suppliers")->findAll();
        $children = array();
        echo "fetched'n";
        echo "'n".count($data)."'n";
        $items = array();
        foreach ($data as $row) {
            foreach ($row->getValue()->getConsigneeName() as $consignee) {
                    $items[] = array(
                        'id' => Util'Util::slugify($consignee),
                        'name' => $consignee,
                        'data' => array(
                            'band' => $row->getValue()->getShipperName(),
                            'relation' => 'Buyer of band'
                        )
                    );
            }
            // echo $row->getValue()->getShipperName()."'n";
        }
        echo "items collected'n".count($items)."'n";

        foreach ($items as &$item) {
            $parent = $item['data'];
            $children[Util'Util::slugify($parent['band'])][] = &$item;
        }
        unset($item);
        foreach ($items as &$item) {
            if (isset($children[$item['id']])) {
                $item['children'] = $children[$item['id']];
            }
        }
        unset($item);
        // die();
        echo "start deleting'n";
        $mongo = new 'MongoClient('mongodb://192.168.125.17:27017');
        $db = $mongo->selectDB('dbname');
        // print_r($db);
        $collection = $db->the_collection;
        // print_r($collection);
        $response = $collection->drop();
        echo "finished'n";
        print_r($response);
        // die();
        echo "starting recording'n";
        $newCollection = $db->createCollection(
            "the_collection",
            array(
                'capped' => true,
                'size' => 1024*1024,
                'max' => 10
            )
        );
        echo "children count ".count($children)."'n";
        $trees = array();
        foreach ($children as $key => $child) {
            $test = array(
                'id' => $key,
                'name' => $key,
                'children' => is_array($child) ? $child : array()
            );
            $serialized = serialize($test);
            $trees[] = $serialized;
            // echo $serialized."'n";
        }
        // die();
        var_dump($trees);
        $newCollection->batchInsert($trees);
        // $dm->getManager()->flush();
        echo "finished'n";