too long

Question

This is my code in controller

public function actionCharges($id){
    $model= \app\models\IpdCharges::findOne(['doctor'=>$id]);
    $model1= \app\models\PatientDetail::findOne(['tpa_name']);
    $query = (new \yii\db\Query())
    ->select('tpa_name')
    ->from('patient_detail') 
    ->innerJoin('daily_ward_entry', 
    'daily_ward_entry.general_regn_no = patient_detail.general_regn_no')
    ->where(['daily_ward_entry.id'=>$id]);


   $command = $query->createCommand();
   $rows = $command->queryAll();
   //var_dump($rows);exit;
    if ($rows === Null){
    echo 'null';exit;
    }else {
       echo 'not null';exit;
       }
    }

If I am checking the var_dump I am getting the null and not null result correctly.

But otherwise I am always getting echoed only 'not null'

what I am doing wrong here.