Druid shows null columns even though is not null is used along with other conditions

[carltal]

Affected Version

Version 25.0.0 and 29.0.1

Description

Please see the following screenshots for details.

When we apply both of these conditions: payment_card_type is not null AND payment_card_type <> 'AMEX', rows with payment_card_type = null will still show up.

When we apply both of these conditions: payment_card_type != 'null' AND payment_card_type <> 'AMEX', rows with payment_card_type = null will still show up.

When we apply only this condition: payment_card_type is not null, rows with payment_card_type = null will NOT show up.