Edit SELECT query Dashlet Home

I have a version of Suite 7.11.8 and I need to modify the SELECT query of the Cases dashlet, in Home, based on filters. I have a particular situation where one of the filters contains an empty value and it does not return any value. Instead, I would like it to return all value that have type’s column = NULL in the DB in that condition. How can I do this?
Thank you,
Giuseppe