Ok, I tried using Spuzzums S_Admin GM_Add code, for some GM problems I've been encountering...but, it reads an runtime error when using the GMS List...why?

runtime error: Cannot read null.len
proc name: Registered GMs (/mob/Admin/verb/gmlist)
source file: Police.dm,1070
usr: Gozelko (/mob/characters/saiyajin)
src: Gozelko (/mob/characters/saiyajin)
call stack:
Gozelko (/mob/characters/saiyajin): Registered GMs()

here's the gmlist code...

gmlist()
set desc = "() Read the list of all GMs' keys"
set category = "Police"
set name="Registered GMs"
if(GMs.len)
usr << "GMs:"
for(var/X in GMs)
usr << "--> [X]"
if(!GMs.len)
usr<<"There are no recorded GMs."

Signed,
Goku72