Filter null values on a Dashboard

Summary:

Hi,

I need to be able to filter for NULL values in a dashboard. Specifically, I have a filter on Gender, which can be NULL or Male/Female, for example.

If I use a filter on the Gender column in the dashboard prompt, it doesn't work for NULL values.

In document Doc ID 2879317.1, I read:
"If you are using this in a prompt, instead of column prompt, a variable prompt should be created to populate a presentation variable with the value that a user has selected/entered. Then this presentation variable should be used in a filter in the analysis and the filter should also include 'Query Type' is NULL condition."