yii2判断数据库字段is null

$query = new Query;              
$query->select('ID, City,State,StudentName') 
      ->from('student')                                
      ->where(['IsActive' => 1]) 
      ->andWhere(['not', ['City' => null]]) 
      ->andWhere(['not', ['State' => null]]) 
      ->orderBy(['rand()' => SORT_DESC])       
      ->limit(10);