[JASS] GetLastCreatedUnit() problem

[Fingolfin]

I use this code snippet for one of my systems:

call GroupAddUnit(g, CreateUnitAtLoc(p, gType(2), l, 0.))
    call SetUnitUserData(GetLastCreatedUnit(), id)
    call BJDebugMsg(GetUnitName(GetLastCreatedUnit()))

But somehow, debug returns null, thus GetLastCreatedUnit is never registered.
is this some bug or do i really have to create the unit first and asign group thereafter for it to work?
I guess it's no big deal, but it's a strange thing it doesent work.