How to set assignment group from a Catalog Item

I have a catalog item called "Self Assigned Task".   I have created a Reference field called "AssignGrp" for this catalog item, which looks up the assignment groups.   I would like to take the group selected during the Request process and have it follow through to the Task.   I am using a workflow to populate other fields down to the Task level, but I cannot get the Assignment group to pass to the task.   The top two lines work fine, the last one does not.   Any help would be appreciated

task.short_description = 'Perform this   ' + current.cat_item.getDisplayValue();

task.description = 'Perform this ' + current.cat_item.getDisplayValue();

task.assignment_group = current.variables.AssignGrp;