Get list of groups by Name - getting empty results from activity class paramter

Hi,

I have used the following in a sample expression rule to get the group name and appending to a group list and working fine

=a!forEach(ri!deletedAMUList,

append(            ri!groupListFordeletedAMU,

getgroupbyname(concat("RTRR"," ",ri!deletedAMUList[fv!index]," ","Landman")),

getgroupbyname(concat("RTRR"," ",ri!deletedAMUList[fv!index]," ","Geologist")),

getgroupbyname(concat("RTRR"," ",ri!deletedAMUList[fv!index]," ","Engineer"))))

Result :

List of Group: 3 items (Group) 624 - RTRR Abbey Landman  (Group) 627 - RTRR Abbey Geologist (Group) 229 - RTRR Abbey Engineer (Group)

But when passing the same to a activity class parameter as an expression and saving to PV (as type group )getting the result as empty ,,,

Thanks

Soujanya