GetSelectedFeatures activity

Hi, I'm trying to use GetSelectedFeatures activity following the example in https://support.geocortex.com/SupportForums/Thread.aspx?thread=55855&mid=2&pageid=0&ItemID=20&pagenumber=1

however, when I run the workflow, I got the following error message "JSON.stringify cannot serialize cyclic structures".  For the input parameters I've tried leave both FeatureSet Collection ID and FeatureSet ID blank, or fill one of them. But got the same error. Has anyone got a working example of the activity? Thanks.

regards,

Jack