Create filter if field value is None OR a specific value

Hello,

I'm trying to display a list of requirements filtered on a custom property I created. The filter correctly lists the possible values, but now I would like to filter the items for which the value in this column is either not set either a specific value. So for example if possible values of myCustomType are "Option1", "Option2" and "Option3" (and obviously, empty string or null, not sure how this is implemented), I would like to display a list of requirements having the value "Option3" or no value, filtering out the ones with value Option1 or Option2. How can this be achieved ?

Thanks ! 

Note: I'm using SpiraTeam 5.2.0.2