How to get null value in drop down when applying filter in Kibana

I am pushing mule logs to elasticsearch. In the logs some fields have no data that means it has null populated in those fields. when ever I want to apply filter on those fields on kibana I am not getting null in the dropdown. Is it not possible to get null in dropdown?
To resolve this I have populated NA in those particular fields then I am able to filter out those. But is that a feasible solution. Any other solution would be greatly helpful.

Thank you.

if the field is not set you could add a filter like field - DOES NOT EXIST (one of the values in the second dropdown on filter editor)