Sokil\Mongo\ExpressionTest::testWhereEmpty PHP Method

    public function testWhereEmpty()
    {
        $document = $this->collection->createDocument(array('f_null' => null, 'f_string' => '', 'f_array' => array()));
        $document->save();
        $documentId = $document->getId();
        // find all rows
        $this->assertEquals($documentId, $this->collection->find()->whereEmpty('f_null')->findOne()->getId());
        $this->assertEquals($documentId, $this->collection->find()->whereEmpty('f_string')->findOne()->getId());
        $this->assertEquals($documentId, $this->collection->find()->whereEmpty('f_array')->findOne()->getId());
        $this->assertEquals($documentId, $this->collection->find()->whereEmpty('f_unexisted_field')->findOne()->getId());
    }