How to do IS NULL and IS NOT NULL with Yii 2 ActiveRecord?

Question

I have a table which has a field `activated_at` timestamp NULL DEFAULT NULL, which means that it can contain a timestamp or it can be null and it\'s

Answer 1

$null = new Expression('NULL');

$query->andFilterWhere(['is not', 'asp_id', $null]);

OR

$query->andFilterWhere(['is', 'asp_id', $null]);