Null value not appears (Checkmk datasource)

Hello,

I’m on Grafana 8.1.3, and my datasource is “checkmk datasource”.

As you can see, with PNP database (or influxdb), the Null values are ok (Blue line).
But with checkmk datasource (yellow line), the Null values not appears.

For me, the reason is because with checkmk datasource we have not “Fill option”.
(Fill : Zero).

Considering that, is it possible with “transform option” to say : “if no value then Zero” ?

Thank you.