Custom variable Comparision (no replies)

Hello,

Iam tracking a custom variable "Card" in Piwik, and I need a count of visitors, where this variable IS and IS NOT set.

But i can't get count for empty variable. It shoud end with == or =@ (contains). IS this syntax correct?

// is not empty    
'segment=customVariablePageName1==Card;customVariablePageValue1!=' // works 

// is empty (does not work)
'segment=customVariablePageName1==Card;customVariablePageValue1==' // returns 0
'segment=customVariablePageName1==Card;customVariablePageValue1=@' // alternative